Unlike the plains and savannahs we crossed yesterday, where the ground is parched up in the dry season, the Atlantic forest, bathed in the rains distilled from the north-east trades, is ever verdant. Perennial moisture reigns in the soil, perennial summer in the air, and vegetation luxuriates in ceaseless activity and verdure, all the year round. Unknown are the autumn tints, the bright browns and yellows of English woods, much less the crimsons, purples, and yellows of Canada, where the dying foliage rivals, nay, excels the expiring dolphin in splendour. Unknown the cold sleep of winter; unknown the lovely awakening of vegetation at the first gentle touch of spring. A ceaseless round of ever-active life weaves the forest scenery of the tropics into one monotonous whole, of which the component parts exhibit in detail untold variety and beauty.
To the genial influence of ever-present moisture and heat we must ascribe the infinite variety of the trees of these forests. They do not grow in clusters or masses of single species, like our oaks, beeches, and firs, but every tree is different from its neighbour, and they crowd upon each other in unsocial rivalry, each trying to overtop the other. For this reason we see the great straight trunks rising a hundred feet without a branch, and carrying their domes of foliage directly up to where the balmy breezes blow and the sun's rays quicken. Lianas hurry up to the light and sunshine, and innumerable epiphytes perch themselves high up on the branches.
The road through the forest was very bad, the mud deep and tenacious, the hills steep and slippery, and the mules had to struggle and plunge along through from two to three feet of sticky clay. One part, named the Nispral, was especially steep and difficult to descend, the road being worn into great ruts. We crossed the ranges and brooks nearly at right angles, and were always ascending or descending. About two we reached a clearing and hacienda, belonging to an enterprising German, named Melzer, near a brook called Las Lajas, who was cultivating plantains and vegetables, and had also commenced brick and tile making, besides planting some thousands of coffee trees. His large clearings were a pleasant change from the forest through which we had been toiling, and we stayed a few minutes at his house. After riding over another league of forest-covered ranges, we reached Pavon, one of the mines of the Chontales Company, and passing the Javali mine soon arrived at Santo Domingo, the headquarters of the gold-mining company whose operations I had come out to superintend.
Geographical position of Santo Domingo.Physical geography.The inhabitants.Mixed races.Negroes and Indians compared.Women.Establishment of the Chontales Gold-Mining Company.My house and garden.Fruits.Plantains and bananas; probably not indigenous to America:propagated from shoots: do not generally mature their seeds.Fig-trees.Granadillas and papaws.Vegetables.Dependence of flowers on insects for their fertilisation.Insect plagues.Leaf-cutting ants: their method of defoliating trees: their nests.Some trees are not touched by the ants.Foreign trees are very subject to their attack.Method of destroying the ants.Migration of the ants from a nest attacked.Corrosive sublimate causes a sort of madness amongst them.Indian plan of preventing them ascending young trees.Leaf-cutting ants are fungus-growers and eaters.Sagacity of the ants.
The gold-mining village of Santo Domingo is situated in the province of Chontales, Nicaragua, in latitude 12 degrees 16 minutes north and longitude 84 degrees 59 minutes west, nearly midway between the Atlantic and the Pacific, where Central America begins to widen out northward of the narrow isthmus of Panama and Costa Rica. It is in the midst of the great forest that covers most of the Atlantic slope of Central America, and which continues unbroken from where we had entered it, at Pital, eastward to the Atlantic; westward it terminates in a sinuous margin about seven miles from the village, and there commence the lightly timbered and grassy plains and savannahs stretching to the Lake of Nicaragua. The surface of the land in the forest region forms a succession of ranges and steep valleys, covered with magnificent timber and much undergrowth. Santo Domingo lies about 2000 feet above the level of the sea, and the hills around it rise from 500 to 1000 feet higher. It is built in the bend of a small stream, the head waters of a branch of the Blewfields river, on a level, low piece of ground, with the brook winding almost round it, and, beyond that, encircled by an amphitheatre of low hills in the hollow of which it lies. The road to the mines runs through it, and forms the main street, having on each side thatched stores and irregularly built houses. The inhabitants, about three hundred in number, are entirely dependent on the mines around, there being no cultivation or any other employment in the immediate neighbourhood. The people are of a mixed descent, in which Indian blood predominates, then Spanish with a slight admixture of the Negro element, whilst amongst the rising generation many fair-haired children can claim paternity amongst the numerous German and English workmen that have been employed at the mines. The store-keepers form the aristocracy of the village. They are indolent; lounging about, or lying smoking in their hammocks the greater part of the day, but generally civil and polite. They are particular in their dress, and may often be seen in faultless European costume, silk umbrella in hand, in twos or threes, taking a short quiet walk up the valley. The lower class of miners are scantily and badly clothed, especially when they come first to the mines. They are bare-footed, with poor ragged cotton trousers and a thin jacket of the same material. Generally, after being a year or two at the mines, they begin to wear better clothing, and may often be seen with a new shirt, which to show off is worn hanging down outside, like a surtout coat. Amongst these are many pure Indians, short sturdy men, who make the steadiest workmen, patient and industrious, but with little appreciation of the value of money, and spending the whole of their wages at the end of the month, before they resume work. At these times the commandant comes in from the town of Libertad, about nine miles distant, with half-a-dozen bare-footed soldiers carrying old muskets on their shoulders, and levies blackmail upon the poor patient "Mosas," as they are called, in the shape of a fine for drunkenness. But the "aguardiente," a native-made rum, is nevertheless always kept on hand, being a government monopoly, and ever ready, so that the Mosas may have no excuse to be sober and escape being fined.
Even in their drink the poor Indians are not very violent, and get intoxicated with surprising stolidity and quietness. Amongst the half-breeds, especially where the Negro element exists, there are often quarrellings and rows, when they slash away at each other with their long knives or "machetes," and get ugly cuts, which, however, heal again quickly.
Both the Negroes and Indians are decidedly inferior to the whites in intellect, but they do not differ so much from the Europeans as they do from each other. The Negro will work hard for a short while, on rare occasions, or when compelled by another, but is innately lazy. The Indian is industrious by nature, and works steadily and well for himself; but if compelled to work for another, loses all heart, and pines away and dies. The Negro is talkative, vivacious, vain, and sensual; the Indian taciturn, stolid, dignified, and moderate. As freemen, regularly though poorly paid and kindly treated, the Indians work well and laboriously in the mines; but the Negro seldom engages either in that or any other settled employment, unless compelled as a slave, in which condition he is happy and thoughtless. I do not defend slavery, but I believe it to be a greater curse to the masters than to the slaves, more deteriorating to the former than to the latter. The Spaniards at first enslaved the Indians, but they died away so rapidly that in a very short time the indigenes of the whole of the once-populous islands of the West Indies were exterminated, and large numbers of Indians were carried off from the mainland to supply their places, but died with equal rapidity; so that the Spaniards found it more profitable to bring negroes from Africa, who thrived and multiplied in captivity as readily as the enslaved Indians pined away and died. In Central America there never were many black slaves; since the States threw off the yoke of Spain there have been none; and this comparative scarcity of the Negro element makes these countries much more pleasant and safer to dwell in than the West Indies, where it is much larger. The Indian seldom or never molests the whites, excepting in retaliation for some great injury; whilst amongst the free Negroes, robbery, violence, and murder need no other incentives than their own evil passions and lust.
The women at Santo Domingo are much the same as those found at all the small provincial towns of Central America. Morality is at a low ebb, and most of them live as mistresses, not as wives, for which they do not seem to suffer in the estimation of their neighbours. This is greatly due in Nicaragua, as it is throughout Central and South America, to the profligate lives led by the priests, who, with few rare exceptions, live in concubinage more or less open. The women have children at an early age, and make kind and indulgent mothers.
The village is bounded to the eastward by the mines and hacienda of the Chontales Mining Company, whose houses, workshops, and machinery are on rising ground on each side of the valley, with the brook running down between. About fifty acres of the forest have been cut down, and a great deal of this is fenced in and covered with grass. Going up the valley from the village, on the right hand side, about fifty yards from the road, on a grass-covered slope, stand the houses of the commissioner and cashier, in the latter of which the medical officer also lives. The former, a large, white-washed, square, two-storied, wooden house, with verandahs round three sides of it, and communicating by a covered passage with a detached kitchen behind, had been built by one of my predecessors, Captain Hill, R.N., who did not live to inhabit it. It was a roomy, comfortable house, commanding a view of the machinery, workshops, and part of the mines on the other side of the valley, and formed my residence for upwards of four years.
The slope in front of the house, down to the river, was covered with weedy bushes when I arrived; but I had these cleared away, and a fine greensward of grass took their place. On this I planted young orange, lime, and citron trees; and I had the pleasure, before I left, to see them beginning to bear their fine fruit. To the west of the house was a dell, covered with fallen logs and rubbish thrown from the hill, in which was a perennial spring of limpid water. I had the logs and rubbish gathered together and burnt, put a light fence round it, and formed a small vegetable, fruit, and flower garden. The mango and avocado trees had not come into bearing before I left; but pineapples, figs, grenadillas, bananas, pumpkins, plantains, papaws, and chioties fruited abundantly. The last named is a native of Mexico; it is a climbing plant with succulent stems and vine-like leaves, and grows with great rapidity. The fruit, of which it bears a great abundance, is about the size and shape of a pear, covered with soft prickles. It is boiled and eaten as a vegetable, and resembles vegetable marrow. At Santo Domingo it continues to bear a succession of fruits during eight months of the year.
Next to maize, plantains and bananas form the principal sustenance of the natives. The banana tree shoots up its succulent stem, and unfolds its immense entire leaves with great rapidity; and a group of them waving their silky leaves in the sun, or shining ghostly white in the moonlight, forms one of those beautiful sights that can only be seen to perfection in the tropics. There are a great many varieties of them, and they are cooked in many ways—boiled, baked, made into pastry, or eaten as a fruit. The varieties differ not only in their fruits, but in the colour of their leaves and stems; the natives can distinguish them without seeing the fruit, and have names for each, by which they are known throughout all Central America, Mexico, and Peru. These names are of Spanish origin; and this fact, together with the absence of any native, Mexican, or Peruvian name for the fruit, inclines me to adopt the opinion of Clavigero, who contends, in opposition to other writers, that the plantain and banana were not known in these countries before the Spanish conquest, but were first brought from the Canaries to Hayti in 1516, and from thence taken to the mainland.
Neither the sugar-cane* nor the plantain is given in the list of the indigenous productions of Mexico by the careful and accurate Hernandez. (* The sugar-cane is said never to bear seed in the West Indies, Malaga, India, Cochin China, or the Malay Archipelago. —Darwin's "Animals and Plants under Domestication" volume 2 page 169.) The natives made sugar from the green stems of the maize. Humboldt thinks that some species of plantain were indigenous to America; but it seems incredible that such an important fruit could have been overlooked by the early historians. In the old world the cultivation of the banana dates from the earliest times of which tradition makes mention. One of the Sanscrit names was bhanu—fruit, from which probably the name "banana" was derived.* (* Humboldt's "Aspects of Nature" volume 2 page 141.)
Both the plantain and the banana are always propagated from shoots or suckers that spring from the base of the plants; and it is to be remarked that the pineapple and the bread-fruit, that are also universally grown from cuttings or shoots, and have been cultivated from remote antiquity, have in a great measure lost the faculty of producing mature seed. Such varieties could not arise in a state of nature, but are due to selection by early races of mankind, who would naturally propagate the best varieties; and, to do this, seed was not required. As the finest kinds of bananas, pineapples, and bread-fruit are almost seedless, it is probable that the nutriment that would have been required for the formation of the seeds has been expended in producing larger and more succulent fruits. We find some varieties of oranges, which also have been cultivated from very early ages, producing fruits without seeds; but as these trees are propagated from seeds, these varieties could not become so sterile as those just mentioned. There can be no doubt that the seedless varieties of banana, bread-fruits, and pineapples have been propagated for hundreds of years; and this fact ought to modify the opinions generally entertained by horticulturists that the life of plants and trees propagated from shoots or cuttings cannot be indefinitely prolonged in that way. Perhaps this may be the case in trees, such as apples, that have come under their notice; and the reason that the varieties die out after a certain time, if not reproduced from seed, may be that the vigour of the trees is at last used up by the production of mature seed, but that in the seedless bananas, pineapples, and bread-fruits this does not happen.
Figs grow well in Nicaragua, and by many their luscious fruit is preferred to all others. My trees suffered greatly from the attacks of a large and fine longicorn beetle (Taeniotes scalaris, Fab.) which laid its eggs in the green bark, and produced white grubs that mined into the stem. I had to dig down to them with a knife to extricate them and prevent them destroying the young trees. We were surrounded at a short distance by the forest, in which grow many species of wild fig-trees; and this probably was the reason that my trees suffered so much, for at Granada the fig-growers were not troubled with this insect.
The grenadilla is the fruit of one of the passion-flowers (Passiflora quadrangularis), and is shaped like a large oblong apple, which it also resembles in perfume. It makes fine tarts and puddings, being somewhat like the gooseberry in taste. I had much difficulty in preserving it from being eaten by small forest rats that came out of the woods, where they had already been accustomed to eat the wild fruit of this climber.
The moist, warm climate seemed to suit the papaw tree, as it grew with great vigour, and produced very large and fine melon-like fruits. The green fruits are excellent for making pastry, if flavoured with a little lime-juice.
In vegetables, I grew three species of sweet potatoes—yellow, purple, and white skinned, and which differ also in their leaves and flowers; cabbages, kidney-beans, pumpkins, yuccas (Jatropha manihot), quequisque (a species of arum, Colocasia esculenta), lettuces, tomatoes, capiscums, endives, parsley, and carrots.
The climate was too damp to grow onions; neither could I succeed with peas, potatoes, or turnips. Scarlet runners (Phaseolus multiflorus) grew well, and flowered abundantly, but never produced a single pod. Darwin has shown that this flower is dependent, like many others, for its fertilisation upon the operations of the busy humble-bee, and that it is provided with a wonderful mechanism, by means of which its pollen is rubbed into the head of the bee, and received on the stigma of the next plant visited.* (* "Gardener's Chronicle" October 24, 1857 and November 14, 1858; also T.H. Farrer in "Annals of Natural History" October 1868.) There are many humble-bees, of different species from ours, in tropical America; but none of them frequented the flowers of the scarlet runner, and to that circumstance we may safely ascribe its sterility. An analogous case has been long known. The vanilla plant (Vanilla planifolia) has been introduced from tropical America into India, but though it grows well, and flowers, it never fruits without artificial aid. It is the same in the hothouses of Europe. Dr. Morren, of Liege, has shown that, if artificially fertilised, every flower will produce fruit; and ascribes its sterility to the absence, in Europe and India, of some insect that in America carries the pollen from one flower to another.* (* Taylor's "Annals of Natural History" volume 3 page 1.) When those interested in the acclimature of the natural productions of one country on the soil of some distant one, study the mutual relations of plants and animals, they will find that in the case of many plants it is important that the insects specially adapted for the fertilisation of their flowers should be introduced with them. Thus, if the insect or bird that assists in the fertilisation of the vanilla could be introduced into and would live in India, the growers of that plant would be relieved of much trouble, and it might be thoroughly naturalised. Judging from my experience, it would be useless to attempt the acclimature of the scarlet-runner bean in Chontales unless the humble-bee were also introduced.
Caterpillars, plant-lice, bugs, and insect pests of all kinds were numerous, and did much harm to my garden; but the greatest plague of all were the leaf-cutting ants, and I had to wage a continual warfare against them. During this contest I gained much information regarding their habits, and was successful in checking their ravages, and I shall occupy the remainder of this chapter with an account of them.
Nearly all travellers in tropical America have described the ravages of the leaf-cutting ants (Oecodoma); their crowded, well-worn paths through the forests, their ceaseless pertinacity in the spoliation of the trees—more particularly of introduced species—which are stripped bare and ragged with the midribs and a few jagged points of the leaves only left. Many a young plantation of orange, mango, and lemon trees has been destroyed by them. Again and again have I been told in Nicaragua, when inquiring why no fruit-trees were grown at particular places, "It is no use planting them; the ants eat them up." The first acquaintance a stranger generally makes with them is on encountering their paths on the outskirts of the forest crowded with the ants; one lot carrying off the pieces of leaves, each piece about the size of a sixpence, and held up vertically between the jaws of the ant; another lot hurrying along in an opposite direction empty-handed, but eager to get loaded with their leafy burdens. If he follows this last division, it will lead him to some young trees or shrubs, up which the ants mount; and then each one, stationing itself on the edge of a leaf, commences to make a circular cut, with its scissor-like jaws, from the edge, its hinder feet being the centre on which it turns. When the piece is nearly cut off, it is still stationed upon it, and it looks as though it would fall to the ground with it; but, on being finally detached, the ant is generally found to have hold of the leaf with one foot, and soon righting itself, and arranging its burden to its satisfaction, it sets off at once on its return. Following it again, it is seen to join a throng of others, each laden like itself, and, without a moment's delay, it hurries along the well-worn path. As it proceeds, other paths, each thronged with busy workers, come in from the sides, until the main road often gets to be seven or eight inches broad, and more thronged than the streets of the city of London.
After travelling for some hundreds of yards, often for more than half a mile, the formicarium is reached. It consists of low, wide mounds of brown, clayey-looking earth, above and immediately around which the bushes have been killed by their buds and leaves having been persistently bitten off as they attempted to grow after their first defoliation. Under high trees in the thick forest the ants do not make their nests, because, I believe, the ventilation of their underground galleries, about which they are very particular, would be interfered with, and perhaps to avoid the drip from the trees. It is on the outskirts of the forest, or around clearings, or near wide roads that let in the sun, that these formicariums are generally found. Numerous round tunnels, varying from half an inch to seven or eight inches in diameter, lead down through the mounds of earth; and many more from some distance around, also lead underneath them. At some of the holes on the mounds ants will be seen busily at work, bringing up little pellets of earth from below, and casting them down on the ever-increasing mound, so that its surface is nearly always fresh and new-looking.
Standing near the mounds, one sees from every point of the compass ant-paths leading to them, all thronged with the busy workers carrying their leafy burdens. As far as the eye can distinguish their tiny forms, troops upon troops of leaves are moving up towards the central point, and disappearing down the numerous tunnelled passages. The out-going, empty-handed hosts are partly concealed amongst the bulky burdens of the incomers, and can only be distinguished by looking closely amongst them. The ceaseless, toiling hosts impress one with their power, and one asks—What forests can stand before such invaders? How is it that vegetation is not eaten off the face of the earth? Surely nowhere but in the tropics, where the recuperative powers of nature are immense and ever active, could such devastation be withstood.
Further acquaintance with the subject will teach the inquirer that, just as many insects are preserved by being distasteful to insectivorous birds, so very many of the forest trees are protected from the ravages of the ants by their leaves either being distasteful to them, or unfitted for the purpose for which they are required, whilst some have special means of defence against their attacks. None of the indigenous trees appear so suitable for them as the introduced ones. Through long ages the trees and the ants of tropical America have been modified together. Varieties of plants that arose unsuitable for the ants have had an immense advantage over others that were more suitable; and thus through time every indigenous tree that has survived in the great struggle has done so because it has had originally, or has acquired, some protection against the great destroyer. The leaf-cutting ants are confined to tropical America; and we can easily understand that trees and vegetables introduced from foreign lands where these ants are unknown could not have acquired, excepting accidentally, and without any reference to the ants, any protection against their attacks, and now they are most eagerly sought by them. Amongst introduced trees, some species of even the same genus are more acceptable than others. Thus, in the orange tribe, the lime (Citrus lemonum) is less liked than the other species; it is the only one that I ever found growing really wild in Central America: and I have sometimes thought that even in the short time since the lime was first introduced, about three hundred years ago, a wild variety may have arisen, less subject to the attacks of the ants than the cultivated variety; for in many parts I saw them growing wild, and apparently not touched. The orange (Citrus aurantium) and the citron (Citrus medicus), on the other hand, are only found where they have been planted and protected by man; and, were he to give up their cultivation, the only species that would ultimately withstand the attacks of the ants, and obtain a permanent footing in Central America, would be the lime. The reason why the lime is not so subject to the attacks of the ants is unknown; and the fact that it is so is another instance of how little we know why one species of a particular genus should prevail over another nearly similar form. A little more or less acridity, or a slight chemical difference in the composition of the tissues of a leaf, so small that it is inappreciable to our senses, may be sufficient to ensure the preservation or the destruction of a species throughout an entire continent.
The ravages of this ant are so great that it may not be without interest for me to enter upon some details respecting the means I took to protect my own garden against their attacks, especially as the continual warfare I waged against them for more than four years made me acquainted with much of their wonderful economy.
In June 1869, very soon after the formation of my garden, the leaf-cutting ants came down upon it, and at once commenced denuding the young bananas, orange, and mango trees of their leaves. I followed up the paths of the invading hosts to their nest, which was about one hundred yards distant, close to the edge of the forest. The nest was not a very large one, the low mound of earth covering it being about four yards in diameter. At first I tried to stop the holes up, but fresh ones were immediately opened out: I then dug down below the mound, and laid bare the chambers beneath, filled with ant-food and young ants in every stage of growth; but I soon found that the underground ramifications extended so far, and to so great a depth, while the ants were continually at work making fresh excavations, that it would be an immense task to eradicate them by such means; and notwithstanding all the digging I had done the first day, I found them the next as busily at work as ever at my garden, which they were rapidly defoliating. At this stage, our medical officer, Dr. J.H. Simpson,* came to my assistance, and suggested pouring carbolic acid, mixed with water, down their burrows. (* This gentleman, beloved by all who knew him, of rare talent, and with every prospect of a prosperous career before him, died at Jamaica from hydrophobia, between two and three months after being bitten by a small dog that had not itself shown any symptoms of that disease.) The suggestion proved a most valuable one. We had a quantity of common brown carbolic acid, about a pint of which I mixed with four buckets of water, and, after stirring it well about, poured it down the burrows; I could hear it rumbling down to the lowest depths of the formicarium four or five feet from the surface. The effect was all I could have wished: the marauding parties were at once drawn off from my garden to meet the new danger at home. The whole formicarium was disorganised. Big fellows came stalking up from the cavernous regions below, only to descend again in the utmost perplexity.
Next day I found them busily employed bringing up the ant-food from the old burrows, and carrying it to a new one a few yards distant; and here I first noticed a wonderful instance of their reasoning powers. Between the old burrows and the new one was a steep slope. Instead of descending this with their burdens, they cast them down on the top of the slope, whence they rolled down to the bottom, where another relay of labourers picked them up and carried them to the new burrow. It was amusing to watch the ants hurrying out with bundles of food, dropping them over the slope, and rushing back immediately for more. They also brought out great numbers of dead ants that the fumes of the carbolic acid had killed. A few days afterwards, when I visited the locality again, I found both the old burrows and the new one entirely deserted, and I thought they had died off; but subsequent events convinced me that the survivors had only moved away to a greater distance.
It was fully twelve months before my garden was again invaded. I had then a number of rose-trees and also cabbages growing, which the ants seemed to prefer to everything else. The rose-trees were soon defoliated, and great havoc was made amongst the cabbages. I followed them to their nest, and found it about two hundred yards from the one of the year before. I poured down the burrows, as before, several buckets of water with carbolic acid. The water is required to carry the acid down to the lowest chambers. The ants, as before, were at once withdrawn from my garden; and two days afterwards, on visiting the place, I found all the survivors at work on one track that led directly to the old nest of the year before, where they were busily employed making fresh excavations. Many were bringing along pieces of the ant-food from the old to the new nests; others carried the undeveloped white pupae and larvae. It was a wholesale and entire migration; and the next day the formicarium down which I had last poured the carbolic acid was entirely deserted. I afterwards found that when much disturbed, and many of the ants destroyed, the survivors migrate to a new locality. I do not doubt that some of the leading minds in this formicarium recollected the nest of the year before, and directed the migration to it.
Don Francisco Velasquez informed me, in 1870, that he had a powder which made the ants mad, so that they bit and destroyed each other. He gave me a little of it, and it proved to be corrosive sublimate. I made several trials of it, and found it most efficacious in turning a large column of the ants. A little of it sprinkled across one of their paths in dry weather has a most surprising effect. As soon as one of the ants touches the white powder, it commences to run about wildly, and attack any other ant it comes across. In a couple of hours, round balls of the ants will be found all biting each other; and numerous individuals will be seen bitten completely in two, whilst others have lost some of their legs or antennae. News of the commotion is carried to the formicarium, and huge fellows, measuring three-quarters of an inch in length, that only come out of the nest during a migration or an attack on the nest or one of the working columns, are seen stalking down with a determined air, as if they would soon right matters. As soon, however, as they have touched the sublimate, all their stateliness leaves them: they rush about; their legs are seized hold of by some of the smaller ants already affected by the poison; and they themselves begin to bite, and in a short time become the centres of fresh balls of rabid ants. The sublimate can only be used effectively in dry weather. At Colon I found the Americans using coal tar, which they spread across their paths when any of them led to their gardens. I was also told that the Indians prevent them from ascending young trees by tying thick wisps of grass, with the sharp points downwards, round the stems. The ants cannot pass through the wisp, and do not find out how to surmount it, getting confused amongst the numberless blades, all leading downwards. I mention these different plans of meeting and frustrating the attacks of the ants at some length, as they are one of the greatest scourges of tropical America, and it has been too readily supposed that their attacks cannot be warded off. I myself was enabled, by using some of the means mentioned above, to cultivate successfully trees and vegetables of which the ants were extremely fond.
Notwithstanding that these ants are so common throughout tropical America, and have excited the attention of nearly every traveller, there still remains much doubt as to the use to which the leaves are put. Some naturalists have supposed that they use them directly as food; others, that they roof their underground nests with them. I believe the real use they make of them is as a manure, on which grows a minute species of fungus, on which they feed;—that they are, in reality, mushroom growers and eaters. This explanation is so extraordinary and unexpected, that I may be permitted to enter somewhat at length on the facts that led me to adopt it. When I first began my warfare against the ants that attacked my garden, I dug down deeply into some of their nests. In our mining operations we also, on two occasions, carried our excavations from below up through very large formicariums, so that all their underground workings were exposed to observation. I found their nests below to consist of numerous rounded chambers, about as large as a man's head, connected together by tunnelled passages leading from one chamber to another. Notwithstanding that many columns of the ants were continually carrying in the cut leaves, I could never find any quantity of these in the burrows, and it was evident that they were used up in some way immediately they were brought in. The chambers were always about three parts filled with a speckled, brown, flocculent, spongy-looking mass of a light and loosely connected substance. Throughout these masses were numerous ants belonging to the smallest division of the workers, which do not engage in leaf-carrying. Along with them were pupae and larvae, not gathered together, but dispersed, apparently irregularly, throughout the flocculent mass. This mass, which I have called the ant-food, proved, on examination, to be composed of minutely subdivided pieces of leaves, withered to a brown colour, and overgrown and lightly connected together by a minute white fungus that ramified in every direction throughout it. I not only found this fungus in every chamber I opened, but also in the chambers of the nest of a distinct species that generally comes out only in the night-time, often entering houses and carrying off various farinaceous substances, and which does not make mounds above its nests, but long, winding passages, terminating in chambers similar to the common species, and always, like them, three parts filled with flocculent masses of fungus-covered vegetable matter, amongst which are the ant-nurses and immature ants. When a nest is disturbed, and the masses of ant-food spread about, the ants are in great concern to carry every morsel of it under shelter again; and sometimes, when I had dug into a nest, I found the next day all the earth thrown out filled with little pits that the ants had dug into it to get out the covered up food. When they migrate from one part to another, they also carry with them all the ant-food from their old habitations. That they do not eat the leaves themselves I convinced myself; for I found near the tenanted chambers, deserted ones filled with the refuse particles of leaves that had been exhausted as manure for the fungus, and were now left, and served as food for larvae of Staphylinidae and other beetles.* (*This theory that the leaf-cutting ants feed on a fungus which they cultivate has been confirmed by Mr. Fritz Muller, who had arrived at it independently in Brazil. His observations on this and various other habits of insects are contained in a letter to Mr. Charles Darwin, published in "Nature" of June 11, 1874.)
These ants do not confine themselves to leaves, but also carry off any vegetable substance that they find suitable for growing the fungus on. They are very partial to the inside white rind of oranges, and I have also seen them cutting up and carrying off the flowers of certain shrubs, the leaves of which they neglected. They are particular about the ventilation of their underground chambers, and have numerous holes leading up to the surface from them. These they open out or close up, apparently to keep up a regular degree of temperature below. The great care they take that the pieces of leaves they carry into the nest should be neither too dry nor too damp, is also consistent with the idea that the object is the growth of a fungus that requires particular conditions of temperature and moisture to ensure its vigorous growth. If a sudden shower should come on, the ants do not carry the wet pieces into the burrows, but throw them down near the entrances. Should the weather clear up again, these pieces are picked up when nearly dried, and taken inside; should the rain, however, continue, they get sodden down into the ground, and are left there. On the contrary, in dry and hot weather, when the leaves would get dried up before they could be conveyed to the nest, the ants, when in exposed situations, do not go out at all during the hot hours, but bring in their leafy burdens in the cool of the day and during the night. As soon as the pieces of leaves are carried in they must be cut up by the small class of workers into little pieces. I have never seen the smallest class of ants carrying in leaves; their duties appear to be inside, cutting them up into smaller fragments, and nursing the immature ants. I have, however, seen them running out along the paths with the others; but instead of helping to carry in the burdens, they climb on the top of the pieces which are being carried along by the middle-sized workers, and so get a ride home again. It is very probable that they take a run out merely for air and exercise. The largest class of what are called workers are, I believe, the directors and protectors of the others. They are never seen out of the nest, excepting on particular occasions, such as the migrations of the ants, and when one of the working columns or nests is attacked; they then come stalking up, and attack the enemy with their strong jaws. Sometimes, when digging into the burrows, one of these giants has unperceived climbed up my dress, and the first intimation of his presence has been the burying of his jaws in my neck, from which he would not fail to draw the blood. The stately observant way in which they stalk about, and their great size, compared with the others, always impressed me with the idea that in their bulky heads lay the brains that directed the community in its various duties. Many of their actions, such as that I have mentioned of two relays of workmen carrying out the ant-food, can scarcely be blind instinct. Some of the ants make mistakes, and carry in unsuitable leaves. Thus grass is nearly always rejected by them, yet I have seen some ants, perhaps young ones, carrying in leaves of grass. After a while these pieces were invariably brought out again and thrown away. I can imagine a young ant getting a severe earwigging from one of the major-domos for its stupidity.
I shall conclude this long account of the leaf-cutting ants with an instance of their reasoning powers. A nest was made near one of our tramways, and to get to the trees the ants had to cross the rails, over which the waggons were continually passing and repassing. Every time they came along a number of ants were crushed to death. They persevered in crossing for several days, but at last set to work and tunnelled underneath each rail. One day, when the waggons were not running, I stopped up the tunnels with stones; but although great numbers carrying leaves were thus cut off from the nest, they would not cross the rails, but set to work making fresh tunnels underneath them. Apparently an order had gone forth, or a general understanding been come to, that the rails were not to be crossed.
These ants do not appear to have many enemies, though I sometimes found holes burrowed into their nests, probably by the small armadillo. I once saw a minute parasitic fly hovering over a column of ants, near a nest, and every now and then darting down and attaching an egg to one entering. Large, horned beetles (Coelosis biloba) and a species of Staphylinus are found in the nests, but probably their larvae live on the rotten leaves, after the ants have done with them.
Configuration of the ground at Santo Domingo.Excavation of valleys.Geology of the district.Decomposition of the rocks.Gold-mining.Auriferous quartz veins.Mode of occurrence of the gold.Lodes richer next the surface than at lower depths.Excavation and reduction of the ore.Extraction of the gold."Mantos".Origin of mineral veins: their connection with intrusionsof Plutonic rocks.
THERE is scarcely any level land around Santo Domingo, but in every direction a succession of hills and valleys. The hills are not isolated; they run in irregular ranges, having mostly an east and west direction, but with many modifications in their trend. From the main valleys numerous auxiliary ones cut deeply into the ranges, and bifurcate again and again, like the branches of a tree, forming channels for carrying off the great quantity of water that falls in these rainy forests. The branching valleys, all leading into main ones, and these into the rivers, have been excavated by subaerial agency, and almost entirely by the action of running water. It is the system that best effects the drainage of the country, and has been caused by that drainage.
The wearing out of valleys near Santo Domingo proceeds more rapidly than in regions where less rain falls, and where the rocks are not so soft and decomposed. Even during the few years I was in Nicaragua there were some modifications of the surface effected; I saw the commencement of new valleys, and the widening and lengthening of others, caused not only by the gradual denudation of the surface, but by landslips, some of which occur every wet season.
The rocks of the district are dolerytes, with bands and protrusions of hard greenstones. The decomposition of the dolerytes is very great, and extends from the tops of the hills to a depth (as proved in the mines), of at least two hundred feet. Next the surface they are often as soft as alluvial clay, and may be cut with a spade. This decomposition of the rocks near the surface prevails in many parts of tropical America, and is principally, if not always, confined to the forest regions. It has been ascribed, and probably with reason, to the percolation through the rocks of rain-water charged with a little acid from the decomposing vegetation. If this be so, the great depth to which it has reached tells of the immense antiquity of the forests.
Gold-mining at Santo Domingo is confined almost entirely to auriferous quartz lodes, no alluvial deposits having been found that will pay for working. The lodes run east and west, and are nearly perpendicular, sometimes dipping a little to the north, sometimes a little to the south, and near the surface, generally turning over towards the face of the hill through which they cut. The trend of the main ranges, also nearly east and west, is probably due to the direction of the outcrops of the lodes which have resisted the action of the elements better than the soft dolerytes. The quartz veins now form the crests of many of the ranges, but are everywhere cut through by the lateral valleys. The beds of doleryte lie at low angles, through which the quartz veins cut nearly vertically. Excepting that they are very irregular in thickness, and often branch and send thin offshoots into the enclosing rocks, they resemble coal seams that have been turned up on edge, so as to be vertical instead of horizontal. They run for a great distance. Near Santo Domingo they had been traced for two miles in length, and probably they extend much further. They are what are called fissure-veins, owing their origin to cracks or fractures in the rocks that have been filled up with mineral substances through chemical, thermal, aqueous, or plutonic agencies. In depth, the bottom of fissure-veins has never been reached, and taking into consideration the deep-seated forces required to produce fissures of such great length and regularity, we may safely assume that they run for miles deep into the earth—that their extension vertically is as great as it is horizontally. The possibility that they extend to immense depths is increased when we reflect that mineral veins occur in parallel groups that run with great regularity for hundreds of miles; and further by the fact that, in all the changes of the earth's surface, by which deep-seated rocks have been brought up and exposed by denudation, no instance is known of the bottom of a fissure-vein having been brought by such movements within the reach of man.
The gold-mines of Santo Domingo are in veins or loads of auriferous quartz that run parallel to each other, and are so numerous that across a band more than a mile in width one may be found every fifty yards. All that have been worked vary greatly in thickness; sometimes within a hundred yards a lode will thicken out from one to seventeen feet. Their auriferous contents vary still more than their width. The richest ore, worth from one to four ounces per ton, occurs in irregular patches and bands very small in comparison with the bulk of the ore stuff, which varies in value from two to seven pennyweights per ton. The average value of all the ore treated by the Chontales Mining Company, up to the end of 1871, has been about seven pennyweights per ton, and during that time small patches have been met with worth one hundred ounces of gold per ton. The gold does not occur pure, but is a natural alloy of gold and silver, containing about three parts of the former to one of the latter. Besides this metallic alloy (to which, for brevity, I shall, in the remarks I have to make, give its common designation of gold), the quartz lodes contain sulphide of silver, peroxide of manganese, peroxide of iron, sulphides of iron and copper, and occasionally ores of lead.
The quartz is generally very friable, full of drusy cavities, and broken up into innumerable small pieces that are often coloured black by the peroxide of manganese. The gold is in minute grains, and generally distributed loosely amongst the quartz. Pieces as large as a pin's head are rare, and specimens of quartz showing the gold in it are seldom met with, even in the richest portions of a lode. The fine gold-dust can, however, easily be detected by washing portions of the lode-stuff in a horn. The quartz and clay is washed away, and the gold-dust sinks to the bottom, and is retained in the horn. This is the usual way in which a lode is tested by the mining agents, and long practice has made them very expert in valuing the ore by the wash in the "spoon." Although most of the gold occurs loose, amongst the soft portions of the lode, the hard quartz also contains it disseminated in minute grains throughout. These can be obtained in the horn by pounding the quartz to powder and then washing it.
One feature in the distribution of gold in the quartz lodes of Santo Domingo led to a most exaggerated opinion of their value when they were first mined by English companies. On the hills, near the outcrops of the lodes, the ore was in some places exceedingly rich. One thousand ounces of gold were obtained from a small patch of ore near the surface of the Consuelo lode, and at Santo Domingo, San Benito, San Antonio, and Javali lodes, very rich ore was also discovered within a few fathoms of the surface. When, however, these deposits were followed downwards, they invariably got poorer, and at one hundred feet from the surface, no very rich ore had been met with. Below that, when the works are prosecuted still deeper, there does not appear to be any further progressive deterioration in the value of the ore, and it varies in yield from two to seven pennyweights of gold per ton, upon which yield further depth does not seem to have any effect. The cause of these rich deposits near the surface does not appear to me to be that the lodes originally, before they were exposed by denudation, contained more gold in their upper portions than below, but to be the effect of the decomposition and wearing down of the higher parts, and the concentration of the gold they contained in the lode below that worn away. We have seen that in the decomposed parts of the lode the gold exists in loose fine grains. During the wet season water percolates freely from the surface down through the lodes, and the gold set free by the decomposition of the ore at the surface must be carried down into it, so that in the course of ages, during the gradual degradation and wearing away of the surface, there has, I believe, been an accumulation of the loose gold in the upper parts of the lodes from parts that originally stood much higher, and have now been worn away by the action of the elements.
This accumulation of loose gold near the surface of auriferous veins, set at liberty from its matrix by the decomposition of the ore, and concentrated by degradation, is probably the reason of the great richness of many of what are called the "caps" of quartz veins; that is, the parts next the existing surface, and has also, perhaps, originated the belief that auriferous lodes deteriorate in value in depth. I at one time, after having studied the auriferous quartz veins of Australia, advocated this theory, which was first insisted upon by Sir R.I. Murchison, but further experience in North Wales, Nova Scotia, Brazil, and Central America has led me to doubt its correctness, excepting in cases such as we have been considering, where there has been an accumulation of gold in the superficial portions of lodes since their original formation. Gold is distributed in quartz veins in bands, and in patches of richer stone of more or less extent. These richer portions of the lodes, if sunk upon perpendicularly, will be passed through, but so also they would be if followed horizontally, their extent in one direction being as great as it is in the other. The chances of meeting with further patches of rich ore in depth, after one has been passed through, are about the same as they are in driving horizontally, and the frequency therefore with which the auriferous ores are met with along the surface will, as a rule, be an index of their occurrence in depth, if we be careful in distinguishing deposits belonging to the original condition of the lodes, and those due to subsequent concentration. To do this we must get below the immediate surface, and take as our guide the gold occurring in the solid undecomposed quartz, and not the loose grains contained in the fissures and cavities.
(PLATE 7. SECTION OF MINE SHOWING METHOD OF EXTRACTING THE ORE.SECTION OF GOLD MINE.Diagram showing method of excavating ore at Santo Domingo Mines.A, Levels.B, Rise, down which the ore is thrown.D, Stopes.C, Stopes refilled with clay and barren rock.Lowest level, Tramway to Stamps.)
The lodes of Santo Domingo are worked by means of levels driven from near the bottoms of the valleys that intersect them. When these levels have entered sufficiently far into the hills, shafts are driven upwards from them to the surface, and other levels driven sixty feet higher than the first. This process is continued until the lode lying above the lowest level has been divided off into horizontal bands, each about sixty feet in depth. The quartz is then excavated above the topmost level, and thrown down the shafts to the lowest, where it is received into waggons and conveyed to the reduction works. As both the ore and the enclosing rocks are greatly decomposed and very soft, the whole of the ground has to be securely timbered as the work proceeds. The levels are timbered with "nispera," a wood of great durability and strength, but the excavated portions between them are only temporarily secured with common soft wood, and at the end of every fortnight filled up with clay and barren rock. The mining is entirely executed by native workmen, principally Mestizos from the border lands of Honduras and Nicaragua, where they have been engaged in silver-mining. They are paid according to the amount of ground excavated, and are very industrious when poor; but when they accumulate a little money, they take fits of idleness and dissipation until it is spent.
The ore is taken down to the reduction works in waggons that run down by gravitation, and are drawn up by mules. It is then stamped to powder by iron beaters, each of which is lifted by cams, and let fall seventy times per minute. The stamped ore, in the form of fine sand, is carried by a stream of water over inclined copper plates covered with mercury, with which is mixed a little metallic sodium. Nearly the whole of the free gold is caught by the mercury, for which it has a great affinity, and accumulates as amalgam on the copper plates, from which it is cleaned off every twelve hours. The sand and water then pass over inclined tables covered with blankets, the fibres of which intercept particles of gold and mercury that have escaped from the first process, and afterwards into a concentrating box, where the coarsest grains of sand and the sulphurets of iron, copper, and silver are caught, and with the sand from the blankets re-treated in arrastres. These arrastres are round troughs, twelve feet in diameter, paved with stones. Four large stones of quartz are dragged round and round in this trough, and grind the coarse sand to fine powder. The gold liberated sinks into the crevices in the stone pavement, a little mercury being put into the trough to form it into amalgam. The arrastres and all the amalgamating apparatus is cleaned up once a month. The amalgam obtained is squeezed through thin dressed skins, and is then of the consistence of stiff putty, and of a silver colour. These balls of amalgam are placed in iron retorts, and the mercury driven off by heat and condensed again in water. The balls of gold so obtained are then melted into bars weighing about one hundred ounces each, and in that state sent to England. At Santo Domingo about two thousand tons of ore are treated monthly, and the whole cost of treatment, including all charges for mining, carriage, reduction, amalgamation, and management, is only about eight shillings per ton. The loss of mercury is about twenty pounds for every thousand tons of ore treated; the smallness of the loss in comparison with that of many other gold-extracting establishments being greatly due to the employment of sodium in the amalgamating process. The loss of mercury usually occurring in amalgamation work is principally caused by its mineralisation, and sodium has such an intense affinity for oxygen and sulphur, that it reduces the mercury to its metallic form again, and prevents its being carried off in light mineralised flakes and powder.
(PLATE 8. SECTION ACROSS SAN ANTONIO LODE.A, Lode.B, Decomposed doleryte.C, Surface soil.D. Quartz rocks in surface soil.)
The band of auriferous quartz veins worked at Santo Domingo continues westward for eight miles, as far as the savannahs near Libertad, and has been largely mined in the neighbourhood of that town, and between that point and Santo Domingo. Besides the working of the mines proper, some surface deposits, called by the Spaniards "Mantos," are also worked for gold, especially in the neighbourhood of Libertad. The "Mantos" consist of broken quartz, covering the faces of the hills in the neighbourhood of some of the lodes. In some places they form a broken but regular stratum over the whole side of a hill, and I was much puzzled at first to account for their origin.
I have already mentioned that the lodes near their summit incline over towards the face of the hill through which they cut. In some cases, as in the San Antonio mine, the lode is in parts bent completely round, as shown in the section in Plate 8. This bending over of the lodes is always towards the face of the hill, and is, I think, produced by successive small landslips. It is evident that if carried still further than in the case shown in the diagram, the lode would be brought down over the face of the hill, and the result has, I think, been achieved in some places, and a regular "Manto" produced. I have already stated that small landslips are of frequent occurrence on the sides of the hills. We had several times the entrance to our mines temporarily closed by them in the wet season.
Mr. David Forbes,* (* "Quarterly Journal of the Geological Society" volume 17.) in his account of the geology of Peru and Bolivia, has advanced the opinion that auriferous quartz veins belong to two different systems, one occurring in connection with Granitic, the other with Diorytic intrusive rocks. In later papers he has shown that this occurrence of gold is not confined to South America, but appears to prevail in all parts of the world.* (* "Geological Magazine" September 1866.) One of the latest writers on the subject, Mr. R. Daintree, in his "Notes on the Geology of Queensland", has shown that the auriferous veinstones in that colony occur in connection with, or in the near vicinity of certain intrusive trap-rocks, and that even some of the trappean dykes themselves are auriferous.* (* "Quarterly Journal of the Geological Society" volume 28 page 308.) Several years ago, I endeavoured to show that mineral veins in granitic districts occurred in regular sequences, with certain intrusive rocks, as follows:—first, Intrusion of main mass of granite; second, Granitic veins; third, Elvan dykes; and, lastly, Mineral veins, cutting through all the other intrusive rocks.* (* See "Geological Survey of Canada" pages 141 and 173.) Later observations have led me to conclude that a similar sequence of events characterised the occurrence of auriferous quartz veins in connection with the intrusive rocks, commonly designated Greenstones, in some districts consisting of diabase, as in North Wales, near Dolgelly; in others of dioryte, as in Santo Domingo; and in many parts of South America and Australia. In North Wales we have, firstly, an intrusion of diabase, occurring in great mountain masses; secondly, Irregular tortuous dykes of diabase; thirdly, Elvan dykes; and, lastly, auriferous quartz veins. In every region of intrusive plutonic rocks that has been thoroughly explored, a similar succession of events, culminating in the production of mineral veins, has been proved to have taken place,* (* "Mineral Veins" page 16.) and it appears that the origin of such veins is the natural result of the plutonic intrusion. There is, also, sometimes a complete gradation from veins of perfectly crystallised granite, through others abounding in quartz at the expense of the other constituents, up to veins filled with pure quartz, as at Porth Just, near Cape Cornwall; and, again, the same vein will in some parts be filled with felspar; in others, contain irregular masses of quartz, apparently the excess of silica beyond what has been absorbed in the trisilicate compound of felspar.* (* Mr. John Phillips in "Memoirs, Geological Survey of Great Britain" volume 2 page 45.) Granitic, porphyritic, and trappean dykes* also sometimes contain gold and other metals; (* Sir R.I. Murchison "Siluria" pages 479, 481, 488 and 500; and R. Daintree "Quarterly Journal of the Geological Society" volume 28 pages 308, 310.) and I think the probability is great that quartz veins have been filled in the same manner—that if dykes and veins of granite have been an igneous injection, so have those of quartz. By an igneous injection, I do not mean that the fused rock owed its fluidity to dry heat. The celebrated researches of Sorby on the microscopical fluid cavities in the quartz of granite and quartz veins, have shown beyond a doubt that the vapour of water was present in comparatively large quantities when the quartz was solidifying. All strata below the surface contain water, and if melted up would still hold it as super-heated steam; and M. Angelot has suggested that fused rock under great pressure may dissolve large quantities of the vapour of water, just as liquids dissolve gases. The presence of the vapour of water would cause the liquefaction of quartz at a much lower temperature than would be possible by heat alone, unaided by water.* (* H.C. Sorby "Journal of the Geological Society" volume 14.) I know that this opinion is contrary to that usually held by geologists, the theory generally accepted being that mineral veins have been produced by deposits from hot springs; but during twenty years I have been engaged in auriferous quartz-mining in various parts of the world, and nowhere have I met with lodes, the phenomena of which could be explained on this hypothesis. The veinstone is pure quartz containing water in microscopical cavities, as in the quartz crystals of granite, but not combined as in the hydrous siliceous sinter deposited from hot springs. The lodes are not ribboned, but consist of quartz, jointed across from side to side, exactly like trappean dykes. There is often a banded arrangement produced by the repeated re-opening and filling of the same fissure; but never, in quartz veins, a regular filling up from the sides towards the centre, as in veins produced by deposits from springs. Quartz veins extend sometimes for miles, and it is necessary to suppose on the hydro-thermal theory that the fissures remained open sufficiently long for the gradual deposition of the veinstones, without the soft and shattered rocks at their sides falling in, nor yet fragments from above; although there are many lodes, fully twenty feet in width, filled entirely with quartz and mineral ores, without any included fragments of fallen rocks, and nowhere showing any trace of regular deposition on the sides. The gold also found in auriferous lodes is never pure, but forms varies alloys of gold, silver, copper, lead, iron, and bismuth; and no way is known of producing these alloys except by fusion.
It is true that mineral veins contain many minerals that could not exist together undecomposed with even a moderate degree of heat; but it is only here contended that the original filling of the lodes was an igneous injection, not that the present arrangement and composition of all the minerals is due to the same action. Since the lodes were first filled they have been subjected to every variety of hydro-thermal and aqueous influence; for the cooling of the heated rocks must have been a slow process, and undoubtedly the veins have often been the channels both for the passage of hot water and steam from the interior, and of cold water charged with carbonic acid and carbonate of lime from the surface, and many changes must have taken place. Auriferous quartz veins have resisted these influences better than others, because neither the veinstone nor the metal is easily altered, and such veins therefore form better guides for the study of the origin of mineral lodes than fissures filled with calc spar and ores of the baser metals, all readily dissolved and re-formed by hydro-thermal agencies. Our mineralogical museums are filled with beautiful specimens of crystals of quartz, fluor spar, and various ores deposited one on the other; and the student who confines his attention to these is naturally led to believe that he sees before him the process by which mineral veins have been filled. But the miner, working far underground, knows that such crystals are only found in cavities and fissures, and that the normal arrangement of the minerals is very different. The deposition of various spars one on the other in cavities is a secondary operation even now going on, and has nothing necessarily to do with the original filling of the lodes; indeed, their arrangement is so different that it helps to prove they have been differently formed.
It would take a volume to discuss this question in all its bearings, and as I have already entered more fully into it in another place,* (* "Mineral Veins" by Thomas Belt. John Weale 1861. ) I shall only now give a brief resume of the conclusions I have arrived at respecting the origin of mineral veins.
1. Sedimentary strata have been carried down, by movements of the earth's crust, far below the surface, covered by other deposits, and subjected to great heat, which, aided by the water contained in the rocks and various chemical reactions, has effected a re-arrangement of the mineral contents of the strata, so that by molecular movements, the metamorphic crystalline rocks, including interstratified granites and greenstones, have been formed.
2. Carried to greater depths and subjected to more intense heat, the strata have been completely fused, and the liquid or pasty mass, invading the contorted strata above it, has formed perfectly crystalline intrusive granites and greenstones.
3. As the heated rocks cooled from their highest parts downwards, cracks or fissures have been formed in them by contraction, and these have been filled from the still-fluid mass below. At the beginning these injections have been the same as the first massive intrusive rocks, either granite or greenstone; but as the rocks gradually cooled, the fissures reached greater and greater depths; and the lighter constituents having been drawn off and exhausted, only the heavier molten silica, mingled with metallic and aqueous vapours, has been left, and with these the last-formed and deepest fissures have been filled. These injections never reached to the surface—probably never beyond the area of heated rocks; so that there have been no overflows from them, and they have only been exposed by subsequent great upheaval and denudation.
4. Probably the molten matter was injected into the fissures of rocks already greatly heated, and the cooling of these rocks has been prolonged over thousands of years, during which the lodes have been exposed to every degree of heat, from that of fusion to their present normal temperature. During the slow upheaval and denudation of the lodes, they have been subjected to various chemical, hydro-thermal, and aqueous agencies, by which many of their contents have been re-arranged and re-formed, new minerals have been brought in by percolation of water from the surrounding rocks, and possibly some of the original contents have been carried out by mineral springs rising through the lines of fissures which are not completely sealed by the igneous injection, as the contraction of the molten matter in cooling has left cracks and crevices through which water readily passes.
5. Some of the fissures may have been re-opened since they were raised beyond the reach of molten matter, and the new rent may have been filled by hydro-thermal or aqueous agencies, and may contain, along with veinstones of calcite derived from neighbouring beds of limestone, some minerals due to a previous igneous injection. Crevices and cavities, called "vughs" by the miners, have been filled more or less completely with crystals of fluor spar, quartz, and various ores of metals from true aqueous solutions, or by the action of super-heated steam.
6. By these means the signs of the original filling of many mineral lodes, especially those of the baser metals, have been obscured or obliterated; but in auriferous quartz lodes both the metal and the veinstone have generally resisted all these secondary agencies, and are presented to us much the same as they were first deposited, excepting that the associated minerals have been altered, and in some cases new ones introduced, by the passage of hot springs from below or percolation of water from the surface.
Climate of the north-eastern side of Nicaragua.Excursions around Santo Domingo.The Artigua.Corruption of ancient names.Butterflies, spiders, and wasps.Humming-birds, beetles, and ants.Plants and trees.Timber.Monkey attacked by eagle.White-faced monkey.Anecdotes of a tame one.Curassows and other game birds.Trogons, woodpeckers, mot-mots, and toucans.
THE climate of Santo Domingo and of the whole north-eastern side of Nicaragua is a very damp one. The rains set in in May, and continue with occasional intermission until the following January, when the dry season of a little more than three months begins. Even during the short-lived summer there are occasional rains, so that although the roads dry up, vegetation never does, the ground in the woods is ever moist, and the brooks perennial. In the shady forest, mosquitoes and sand-flies are rather troublesome; but the large cleared space about the houses of the mining company is almost free from them, and in the beautiful light evenings one can sit under the verandahs undisturbed, watching the play of the moonbeams on the silky leaves of the bananas, the twinkling north star just peeping over the range in front, with "Charlie's Wain" in the upper half of its endless circlings, whilst in the opposite direction the eye rests on the beautiful constellations of the southern hemisphere. On the darkest nights innumerable fire-flies flash their intermittent lights as they pass amongst the low bushes or herbage, making another twinkling firmament on earth. On other evenings, sitting inside with lighted candles and wide opened doors, great bats flap inside, make a round of the apartment, and pass out again, whilst iris-winged moths, attracted by the light, flit about the ceiling, or long-horned beetles flop down on the table. In this way I made my first acquaintance with many entomological rarities.* (* In moths, numerous fine Sphingidae and Bombycidae; and in beetles, amongst many others, the rare Xestia nitida (Bates) and Hexoplon albipenne (Bates) were first described from these evening captures.)
The heaviest rains fall in July and August, and at these times the brooks are greatly swollen. The one in front of my house sometimes carried away the little wooden bridge that crossed it, and for an hour or two became impassable, but subsided again almost as soon as the heavy rain ceased falling, for the watershed above does not extend far. Every year our operations were impeded by runs in the mines, or by small landslips stopping up our tramways and levels, or floods carrying away our dam or breaking our watercourses; but after August we considered our troubles on this score at an end for the season. Occasionally the rains lasted three or four days without intermission, but generally they would come on in the afternoon, and there would be a downpour, such as is only seen in the tropics, for an hour or two, then some clear weather, until another great bank of clouds rolled up from the north-east and sent down another deluge. In September, October, and November there are breaks of fine weather, sometimes lasting for a fortnight; but December is generally a very wet month, the rains extending far into January, so that it is not until February that the roads begin to dry up.
I had much riding about. The mines worked by us, when I first went out, extended from Consuelo, a mile higher up the valley, to Pavon, a mile below Santo Domingo; and even after I had concentrated our operations on those nearer to our reduction works, there were many occasions for me to ride into the woods. I had to look after our wood-cutters and charcoal-burners, to see that they did not encroach upon the lands of our neighbours, as they were inclined to do, and involve us in squabbles and lawsuits; paths had to be opened out, to bring in nispera and cedar timber, our property surveyed, and new mines, found in the woods, visited and explored. Besides this, I spent most of my spare time in the forest, which surrounded us on every side. Longer excursions were frequent. The Nicaraguans, like all Spanish Americans, are very litigious, and every now and then I would be summoned, as the representative of the company, to appear at Libertad, Juigalpa, or Acoyapo, to answer some frivolous complaint, generally made with the expectation of extorting money, but entertained and probably remanded from time to time by unscrupulous judges, who are so badly paid by the government that they have to depend upon the fees of suitors for their support, and are much open to corruption. These rides and strolls into the woods were very fruitful in natural-history acquisitions and observations. I shall give an account of some of those made in the immediate vicinity of Santo Domingo, and I wish I could transfer to my readers some of the pleasure that they afforded me. They gave the relief that enabled me to carry on for years an incessant struggle, under great difficulties, to bring the mines into a paying state, continually hampered for want of sufficient capital, with most inadequate machinery, and all the annoyances, delays, and disappointments inevitable in carrying on such a precarious enterprise as gold-mining far in the interior of a half-civilised country.
The brook that ran at the foot of the bank below my house, and there called the "Quebrada de Santo Domingo," is dignified half a mile lower down, after passing the mines of the Javali Company and receiving the waters of another brook coming down from the westward, by the name of the Javali river. The Indians, however, both at the Indian village of Carca, seven miles back in the mountains, and those lower down the river itself, call it "Artigua." The preservation of these old Indian names is important, as they might some time or other throw considerable light on the early inhabitants of the country. In all parts of the world the names of mountains, valleys, lakes, and rivers are among the most certain memorials of the ancient inhabitants. The reason the names of the natural features of a country remain unchanged under the sway of successive nations, speaking totally different languages, appears to be this. The successful invaders of a country, even in the most cruel times, never exterminated the people they conquered; at the least, the young women were spared. The conquerors established their own language, and to everything they had known in their own land they gave their own names; but to things quite new to them, which nearly always included the mountains, valleys, lakes, and rivers, and often the towns and many of the natural productions, they accepted the existing names from the survivors of the conquered people. Often the names were corrupted, the new inhabitants altering them just a little, to render their pronunciation easier, or to make them significant in their own language. Thus the fruit of the Persea gratissima was called "ahuacatl" by the ancient Mexicans; the Spaniards corrupted it to "avocado," which means an advocate; and our sailors still further, to "alligator pears." The town of Comelapa, in Chontales, the name of which means, in Spanish, "Eat a macaw," is undoubtedly a corruption of some old Indian name of similar form to that of the neighbouring village of Comoapa, although the Spaniards give an absurd explanation of it, evidently invented, according to which it was so called because a sick man was cured of a deadly disease by eating the bird indicated.
The Artigua—I shall call it so, to do what I can to save the name from oblivion—is woefully polluted by the gold-mining on its banks, and flows, a dark muddy stream, through the village of Santo Domingo, and just below it precipitates itself one hundred and twenty feet over a rocky fall. One of the forest roads leads down its banks for several miles to some small clearings, where a few scattered, Spanish-speaking Indians and half-breeds cultivate maize and plantains. After leaving Santo Domingo, it at first follows the left bank of the stream, through low bushes and small trees of second growth, then crosses a beautiful clear brook coming down from the east, and finally winding round a slope covered with great trees and dense undergrowth, reaches the site chosen for the machinery at Pavon, where a large space has been cleared, much of which is covered with grass. After descending a steep hill, the Artigua, with its muddy water, is crossed. Here, in the dry season, in the hot afternoons, the wet sandy banks were the favourite resorts of multitudes of butterflies, that gathered in great masses on particular moist spots in such numbers that with one swoop of my net I have enclosed more than thirty in its gauzy folds. These butterflies were principally different species of Callidryas, yellow and white, mixed with brown and red species of Timetes, which, when disturbed, rose in a body and circled about; on the ground, looking like a bouquet; when rising, like a fountain of flowers. In groups, by themselves, would be five or six specimens of yellow and black Papilios, greedily sucking up the moisture, and vibrating their wings, now and then taking short flights and settling again to drink. Hesperidae, too, abounded; and in a favourable afternoon more than twenty different species of butterflies might be taken at these spots, the finest being a lovely white, green, and black swallow-tailed Papilio, the first capture of which filled me with delight. Near the river were some fallen-down wooden sheds, partly overgrown with a red-flowered vine. Here a large spider (Nephila) built strong yellow silken webs, joined one on to the other, so as to make a complete curtain of web, in which were entangled many large butterflies, generally forest species, caught when flying across the clearing. I was at first surprised to find that the kinds that frequent open places were not caught, although they abounded on low white-flowered shrubs close to the webs; but, on getting behind them, and trying to frighten them within the silken curtain, their instinct taught them to avoid it, for, although startled, they threaded their way through open spaces and between the webs with the greatest ease. It was one instance of many I have noticed of the strong instinct implanted in insects to avoid their natural enemies. I shall mention two others. The Heliconidae, a tribe of butterflies peculiar to tropical America, with long, narrow, weak wings, are distasteful to most animals: I have seen even spiders drop them out of their webs again; and small monkeys, which are extremely fond of insects, will not eat them, as I have proved over and over again. Probably, in consequence of this special protection, they have not needed stronger wings, and hence their weak flight. They are also very bold, allowing one to walk close up to flowers on which they alight. There is one genus with transparent wings that frequents the white-flowered shrubs in the clearings, and I have sometimes advanced my hand within six inches of them without frightening them. There is, however, a yellow and black banded wasp that catches them to store his nest with; and whenever one of these came about, they would rise fluttering in the air, where they were safe, as I never saw the wasp attack them on the wing. It would hawk round the groups of shrubs, trying to pounce on one unawares; but their natural dread of this foe made it rather difficult to do so. When it did catch one, it would quietly bite off its wings, roll it up into a ball, and fly off with it. Again, the cockroaches that infest the houses of the tropics are very wary, as they have numerous enemies—birds, rats, scorpions, and spiders: their long, trembling antennae are ever stretched out, as if feeling the very texture of the air around them; and their long legs quickly take them out of danger. Sometimes I tried to chase one of them up to a corner where on the wall a large cockroach-eating spider stood motionless, looking out for his prey; the cockroach would rush away from me in great fear; but as soon as it came within a foot of its mortal foe nothing would force it onwards, but back it would double, facing all the danger from me rather than advance nearer to its natural enemy.