GEOLOGY OF THE DIGGINGS.
When a man of observation walks over the Gold Fields, his attention is arrested by the following facts.
1. The prevalent rocks are observed to be of a crystalline, or what is called igneous, character; as, granites of all varieties, quartz, mica, slate, felspar, sienite &c. Some felspar is seen decomposed into a soft white finger-staining mineral, or into fine porcelain clay. At the “Gap” of the river Macquarie the sienite is flanked by precipitous silicious slates. The Mount Alexander range is of a granitic character, and the beds of the streams running from it, on the Bendigo road, are filled with huge boulders of granite on a granite floor, containing parallel veins of crystallized felspar, having usually a north and south direction. No detritus of other rocks is found on the granite by the “Porcupine.” Some of the rocks bear fantastic resemblance to Beehives, Logan stones, and Scandinavian Tumuli. Granite is the bed of the Macquarie at Bathurst, and the base of the Mullion range, near which were the first diggings of New South Wales. The quartz is of all kinds; black, white, yellow, pink, green, red, spotted, streaked, mosaic, porous, fibrous, clinker like, and crystallized. Carbon makes it black; copper or chlorine, green; oxide of iron, red or brown; manganese, rose colour. The crystals are hexaedron pyramids, single or double, of different sizes and degrees of transparency. Some rise from the surface like wedges, having a singular appearance. The prisms are triangular, quadrilateral or pentagonal; some crystals have others attached to their sides. Veins of black quartz are observed with the centre very vesicular. Carious quartz, or swimming stone, is not common. The granulated quartz or grindstone schist has often minute transparent crystals in cavities. From a hole in Golden Gully, Bendigo, I obtained a specimen of soft sandstone, with most exquisitely beautiful veins of crystallized quartz running in all directions.
2. The Crystalline rocks are observed gradually changing into what is called the Sedimentary rocks, as slates. Such a transition from the crystalline to the laminated form is by insensible degrees. The experience of the miner is often opposed to the theories of geologists. He cannot help noticing the different kinds of slates, as presenting proof of their being transmutations of, or some among the many kinds of developement in, crystalline rocks. There are slates as amorphous looking as any Huttonian can desire. Others are so silicious, as to be denominated by the New South Wales geologists,Quartzites. On the Bell’s creek the clay slate changes into jasper. The chlorite slate of Ophir is so full of quartz veins, and dykes and bosses of quartz, as to be called by Sir T. L. Mitchell,Quartz iferons schist. Instances are numerous of slate with embedded quartz, and quartz entangling slate. At the cathedral rock, near Specimen Hill, Bendigo, numerous veins of chlorite slate are seen running unharmed and unchanged amidst that huge block of so called, igneous rock. The same specimen of quartz has exhibited in different parts not only different colours, but the clinker, the calcined, and the transparent conditions. The Rev. W. B. Clarke, of Sydney, hints at the probability of quartz, greenstone, basalt, and slates, by the influence of segregation, chemical affinity, galvanic or other forces, being “derived from the same original source, and indefinitely varied in the order of their arrangements and relations to each other at different intervals.” Mr. Clarke’s observations on the Diggings’ ground, would seem rather to have confounded his geological creed. The absence of ordinary stratification, even in the holes, is a remarkable feature. The character of stuff through which we have to go on the tops of hills resembles that in the gullies. Though much of the soil bears evidence of diluvial action, yet a considerable portion clearly results from the decomposition of the rocks near. The great irregularity of mineral beds in the holes, no two holes being alike, would not present the idea of gentle depositions, nor are we warranted to assume volcanic dislocation. Such fantastic changes in the order and depths of these mineral beds, were compared by a diggings’ friend to the alternations of the eight notes of music in different bars.
Our slates in Victoria are elongated, amorphous, crystalline, contorted, laminated, with or without cleavage, red, brown, white, blue, and chocolate color. Some are very talcose and soapy. In others grains or streaks like rainbows are seen. Mundic or Iron pyrites’ crystals are found in dark, friable, unctious slate of Forest creek. At Miles’ creek, Bendigo, are fine curvillinial lines in red slates. Near the old square, Forest creek, and beside Fryer’s creek is some splendid blue book slate, resembling the leaves of a book. The cleavage of the slates is evidently made by magnetic agency. Sometimes, as at Bendigo, the cleavage planes preserve a true parallelism while passing through contorted hard slate.
3. The rocks of the diggings are observed in successive bands of various colors and compositions with a great vertical inclination. This is the same as in other gold countries. Intelligent miners are much struck with this fact of rock succeeding rock over a country side by side, and all with a perpendicular direction. The slate has some odd changes of position, influenced doubtless by local disturbances. On the road from Bendigo to Bullock creek, the rock may be seen in one place dipping 80° to the east, a little further 80° to the west, then 10° to the west, &c. In Iron bark gully I noticed in a square yard of space the following different position, in some blue roofing slate; 45° to N E, 30° to Es 70° to N. The Pipe clay, which, being silicate of alumina, is decomposed from siliceous slates and granites, has, like the neighbouring rocks, this same vertical inclination.
4. The ridges of rocks are observed to run nearly in a North and South direction. This is the same as in all gold countries, and establishes the theory of terrestrial magnetic agency.
5. There is a remarkable abundance of iron. Crystals of iron pyrites are common. The carburet of iron or emery, like iron sand, is always associated with gold. Oxydulous masses of iron form a precipitous waterfall of 60 feet near Oaky Creek, New South Wales. Ferruginous, or iron bearing, conglomerate, overhangs the river at Ophir. Auriferous bands of argillaceous iron ore traverse the limestone of Bungonia. Large nodules of peroxide of iron, and magnetic iron ore of all kinds, are taken out of our Victoria Diggings. The burnt stuff, or burnt quartz of the miners, is a ferruginous cement binding quartz pebbles. There is no need of referring this compound to volcanic or electric fire. Chemical action with moisture will make any mixture hard enough. Roman cement when dried is not very soft. In the Ballarat holes the “Burnt Quartz” has been found ten feet thick; it is less at the Mount, and less still at Bendigo, though on some Bendigo hills it occurs six or eight feet.
6. The Gold is found in positions where there is a transition from the ordinary crystalline rocks to those of the sedimentary character. This remark leads us at once to the interesting and debated subject of the “Origin of Gold.” Some say that the gold of our gullies and hills is washed down from a matrix or source,—that is from certain golden lodes in a mountain. Others affirm that a volcano once burst forth and showered gold instead of cinders, and they direct us to the shot like appearance of nuggets. It is believed, also, that mica is the mother of Gold. Without doubt some is washed down by rivers, and more was deposited by ancient floods when covering the whole country, but a large amount is foundin situas it always had been. It is assuredly a fact noticed in all auriferous countries, that the gold is seen in positions where the sedimentary looking rocks come in contact with the so called igneous rocks. It is also, always found associated with iron, and commonly in the decomposition of rocks. It is in auriferous sulphuret of iron in Chili; ochreous decomposed silicious rock, adhering to specular iron, in Columbia; ferruginous sands in the Niger; decomposed reddish granite in Thibet; honeycomb quartz and rotten slate in Virginia; black peroxide of iron in Ceylon; pyrites in decomposed felspar in Hungary; sulphuret of iron in quartz in France; ferruginous clay slate in Granada; with iron of all kinds in Wieklow; decomposed crystalline rock with iron pyrites in the Ural; so in California, so in Australia. It would appear, then, that the gold was the produce of certain changes in certain rocks. The formation of crystals is somewhat analogous. The wall of a mine previously bare is seen gradually to get covered with crystals. Even crystals of iron pyrites are so produced, and are known by miners as “Young Mundic.” There must be, then, constant activity going on in the apparently inert mass of mineral matter. There is no rest in creation. The heavens above us speak of eternal movement. The animal and vegetable kingdoms reveal an incessant round of change. And now the dull rock unfolds to us the existence of motions and transformations that know no stay. There may be death upon the earth, there can be none beneath. We sweep off crystals only to make way for more. And may it not be so with metals in general? We may not know the particular elements and circumstances necessary for the formation of the yellow treasure, but some approximate conception may be gained by observation.
If crystals are the flowers of the earth beneath, metals are unquestionably mineral trees in gradual development, and dependent upon certain acids, alkalies, and other materials, for sources of their transformations. Moisture seems essential for these chemical changes. The production of gold is observed to take place chiefly towards the surface, though at a considerable depth in the compact rock very minute particles may be detected. When the crystalline rock disintegrates, iron sand is developed and accumulated. Mr. Hopkins, of the Port Phillip Gold Company, the ablest practical mining geologist of the day, and who calls clay slate “oxidated crust of granite,” observes, that it is “within the limits of this transition of the crystalline base into the oxydated compound that the minerals become principally developed in veins, &c.” An interesting illustration of this is afforded at Specimen Hill, Bendigo, where the metal lies between the quartz and the slate. Again, at Clunes, the fissures in the quartz are filled with greasy red earth, highly impregnated with iron, and in this was the gold. Sir T. L. Mitchell, in his most interesting report, tells us, that the gold of Summerhill Creek was “in incrementitious portions and separate increments of quartzose crystals.” In fact, the metal is often detected in considerable masses in the solid rock apart from any veins, which could not be, unless formed in the very place. It is not often, however, that a lump of 106lbs, as at Louisa Creek, is found thus detached.
Our Gold deposits of Victoria, then, are not the products of washings from distant rocks, but of certain friable metalliferous rocks, which gradually wearing away unfold their treasures; and the gold itself is a sort of crystallization or growth in ferruginous crystalline formations, acting under regular, though at present unknown laws.Our rocks are at this moment producing gold.The metal is found on the tops of hills and in all possible situations. We never are sure where to drop on it. All we see is thatwhere it is, there it is. In some gullies the sides of the hills are not favorable; in others they are. Long Gully, Bendigo, received a return of visitors, after beingwrought out, to have the hills ransacked. Then, with regard to the Pipe clay, the gold is in it, on it, or under it, according to the locality; that is, according to the period when the metal was formed, and rolled off from the parent rock, whether before, or after, or during the development of the decomposed felspar. Some men who came down to pipe clay in a certain gully found no gold, and retired. Another party pierced through the white floor, and brought up the wealth. In Californian gully more than six feet of it contained gold. The pipe clay varies much in depth, from an inch to forty feet. Occasionally, as in the shallow, lucky, holes of Peg Leg Gully, there is no pipe clay at all. The character of the gold changes according to the locality in which the transmuting agency has been more or less active. The lumps, however, are not larger in proportion to proximity to some matrix, as supposed, or when nearer to the volcano, which others think threw out the lovely, weighty, cinders. Notwithstanding all this uncertainty which exists as to the whereabouts of gold, I believe that with the progress of science it will be quite possible at once to know the precise place in which to discover the hidden beauties. O the delicious yellow crystals! Who does not love to view them, whether in the form of fibres, scales, or nuggets! The poet well may sing;
Or 'midst the darksome wondersWhich earth’s vast caves conceal,Where subterranean thundersThe miner’s path reveal;Where bright in matchless lustre,The lithal flowers (crystals) unfold,And 'midst the beauteous cluster,Beams efflorescent Gold.
Or 'midst the darksome wondersWhich earth’s vast caves conceal,Where subterranean thundersThe miner’s path reveal;Where bright in matchless lustre,The lithal flowers (crystals) unfold,And 'midst the beauteous cluster,Beams efflorescent Gold.
Or 'midst the darksome wondersWhich earth’s vast caves conceal,Where subterranean thundersThe miner’s path reveal;Where bright in matchless lustre,The lithal flowers (crystals) unfold,And 'midst the beauteous cluster,Beams efflorescent Gold.
Or 'midst the darksome wonders
Which earth’s vast caves conceal,
Where subterranean thunders
The miner’s path reveal;
Where bright in matchless lustre,
The lithal flowers (crystals) unfold,
And 'midst the beauteous cluster,
Beams efflorescent Gold.
[ADVERTISEMENT.]