CHAPTER VI.

[59]I would refer the student for a fuller consideration of the phenomena thus briefly noticed, to the 6th edition of my Wonders of Geology, pp. 669, 718, 731.

I will conclude this chapter with the following beautiful reflections of Dr. Buckland on the origin and nature of Coal,and the changes it undergoes when rendered subservient to the necessities and luxuries of man.

"Few persons are aware of the remote and wonderful events in the economy of our planet, and of the complicated applications of human industry and science, which are involved in the production of the coal that supplies with fuel the metropolis of England.

"The most early stage to which we can carry back its origin, was among the swamps and forests of the primeval earth, where it flourished in the form of gigantic Calamites, and statelyLepidodendra, andSigillariæ. From their native bed, these plants were transported into some adjacent lake, or estuary, or sea. Here they floated on the waters, until they sank saturated to the bottom, and being buried in the detritus of adjacent lands, became transferred to a new estate among the members of the mineral kingdom. A long interment followed, during which a course of chemical changes, and new combinations of their vegetable elements, converted them to the mineral condition of coal. By the elevating force of subterranean agency, these beds of coal have been uplifted from beneath the waters, to a new position in the hills and mountains, where they are accessible to the industry of man. From this fourth stage, coal has been removed by the labours of the miner, assisted by the arts and sciences, that have co-operated to produce the steam-engine, and the safety-lamp. Returned once more to the light of day, and a second time committed to the waters, it has, by the aid of navigation, been conveyed to the scene of its next and most considerable change by fire; a change during which it becomes subservient to the most important wants and conveniences of man. In this seventh stage of its long eventful history, it seems, to the vulgar eye, to undergo annihilation; its elements are, indeed, released from the mineral combinations which they have maintained for ages, but their apparent destruction is only the commencementof new successions of change and of activity. Set free from their long imprisonment, they return to their native atmosphere, from which they were absorbed by the primeval vegetation of the earth. To-morrow they may contribute to the substance of timber, in the trees of our existing forests; and having for a while resumed their place in the living vegetable kingdom, may, ere long, be applied a second time to the use and benefit of man. And when decay or fire shall once more consign them to the earth, or to the atmosphere, the same elements will enter on some further department of their perpetual ministration in the economy of the material world."[60]

[60]Bd p. 481.

FOSSIL VEGETABLES.

In the present section of this work, I propose to explain the botanical arrangement and nomenclature of fossil plants; and figure and describe one or more species of the genera that are most likely to come under the observation of the student, either in public or private collections, or in the course of his researches in the field.

To determine the botanical relations of fossil leaves and stems, reference must be had to works expressly devoted to the subject; namely, the "British Fossil Flora," by Dr. Lindley and Mr. Hutton, and the "Histoire des Végétaux Fossiles," by M. Adolphe Brongniart. The classification of the last-named eminent botanist is here adopted, as the most easy of application.

With regard to the nomenclature, it may be necessary to remark, that when a fossil plant undoubtedly belongs to a recent genus, the usual botanical name is employed: for example,Equisetum Lyellii; when the fossil does not possess all the generic characters, yet is evidently allied to a recent genus, the termites(from λιθος,lithos, stone), is added—asEquisetites,Palmacites, &c.; and this termination is invariably adopted by some authors. When the fossil plant differs altogether from any known type, it is distinguished by some arbitrary generic name, asBucklandia,Sigillaria, &c.

There are also a few provisional genera for the receptionof fossil leaves, fruits, and stems, whose characters and relations are but imperfectly known; as Carpolithes, Endogenites, &c. Upon these principles the present arrangement has been founded: the progress of discovery will, of course, be continually adding to the list, and the classification require to be modified.

FOSSIL CRYPTOGAMIA.

The following account of the principal types of the ancient floras whose relics are preserved in the mineral kingdom, though commencing with those of the most simple structure, theCryptogamia, and advancing to the higher orders, is not strictly botanical; for it was found convenient, in some instances, to notice certain species and genera of different orders under the same head, from their occurrence in the same geological formations.

It is estimated that not more than two thousand species of plants have been discovered in a fossil state, while the known recent species amount to upwards of eighty thousand.

Cellular Cryptogamia; Algæ.—The plants designated by botanistsAlgæ, and commonly known as sea-weeds, lavers, and fresh-water mosses, are of the most simple structure—mere aggregations of cells—but present innumerable varieties of form and magnitude: many species are mere vesicles of such minuteness as to be invisible to the unassisted eye, except accumulated in countless myriads, when they appear as a green, purple, or reddish, slime in the water; or as a film on wood or stone, or on the ground, in damp situations; while others are tough branched marine plants, many fathoms in length.

The Algæ form three principal groups: 1. thejointless, as the Fuci, the Dulses, Tangles, and Lavers: 2. thejointed, which are composed of thread-like articulated tubes; such are the fresh-water Confervæ: 3. thedisjointed, or Brittle-worts, so called from their spontaneous self-division, which is in some kinds complete, in others only partial; and these,by separating transversely, and leaving each cell or frustule attached at the angles, produce those beautiful chains of angular green transparent cases, so constantly seen under the microscope when substances from fresh-water streams or lakes are submitted to examination.

As many of these forms are endowed with spontaneous motion, and possess other properties common to animal organization, it is not surprising that their vegetable nature was doubted, and that even so profound a naturalist as M. Ehrenberg placed them in the animal kingdom: the greater number being comprised in his family ofBacillariæ, were described in the former edition of this work, as Infusoria or Animalcules; in conformity with the classification of the illustrious microscopist, whose splendid works and indefatigable labours have so greatly promoted the advancement of microscopical investigation.[61]

[61]The whole of the objects calledInfusoriain the first edition of "The Medals of Creation" belong to various kinds of Diatomaceæ.

FOSSIL DIATOMACEÆ.

These minute vegetable organisms are placed by botanists in two tribes, theDiatomaceæor theBrittle-worts, and theDesmidieæ. The latter are exclusively inhabitants of fresh-water, while a large proportion of the former are marine plants. Some naturalists (M. Brébisson) restrict the nameDiatomaceæto those species which secrete siliceous envelopes; and that ofDesmidieæto those whose structures are not siliceous, and are reducible by heat to carbon. As the durable parts of these plants alone concern the geologist, the nameDiatomaceæwill be employed as a general term in reference to their fossil remains.

These tribes of Algæ abound in every lake and stream of fresh-water, in every pool or bay, and throughout the ocean from the equator to the poles. Certain kinds of sea-weeds secrete carbonate of lime; but the Diatomaceæ have the power of separating silex, or the earth of flint, from thewater, by some unknown process, and their tissues are composed of pure quartz: hence, under the microscope, their remains, consisting wholly of rock crystal, exhibit the most exquisite forms, elaborately fretted and ornamented (seeLign. 4). After the death and decomposition of these plants, their durable frustules or cases appear as colourless discs, cups, spheres, shields, &c., and these accumulate at the bottom of the water in such inconceivable numbers, as to form strata of great thickness and extent. Slowly, imperceptibly, and incessantly, are the vital energies of these atoms separating from the element in which they live the most refractory and enduring of mineral substances, silex, and elaborating it into imperishable structures, and thus adding enormous contributions to the accumulations of detritus, which make up the sedimentary rocks of the crust of the globe.

The extent of this infinitesimal flora throughout regions where no other forms of vegetation are known, is strikingly demonstrated by the observations of our eminent botanical traveller. Dr. Joseph Hooker, in his account of the Antarctic regions.[62]

[62]"On the Botany of the South Polar Regions;" in Sir J. Ross's Voyage of Discovery.

"Everywhere," Dr. Hooker states, "the waters and the ice alike abound in these microscopic vegetables. Though too small to be visible to the unassisted eye, their aggregated masses stained the iceberg and pack-ice wherever the latter were washed by the sea, and imparted a pale ochreous colour to the ice. From the south of the belt of ice which encircles the globe, to the highest latitudes reached by man, this vegetation is everywhere conspicuous, from the contrast between its colour and that of the white snow and ice in which it is imbedded.

"In the 80° of south latitude all the surface ice carried along by currents, and the sides of every berg, and thebase of the great Victoria barrier itself—a perpendicular wall of ice, from one to two hundred feet above the sea level—were tinged brown from this cause, as if the waters were charged with oxide of iron. The majority of these plants consist of simple vegetable cells enclosed in indestructible silex; and it is obvious that the death of such multitudes must form sedimentary deposits of immense extent.

"The universal existence of such an invisible vegetation as that of the Antarctic Ocean is a truly wonderful fact, and the more so from its being unaccompanied by plants of a high order. This ocean swarms with mollusca, and entomostracous crustaceans, small whales, and porpoises; and the sea with penguins and seals, and the air with birds; the animal kingdom is everywhere present, the larger creatures preying on the smaller, and these again on those more minute; all living nature seems to be carnivorous. This microscopic vegetation is the sole nutrition of the herbivorous animals; and it may likewise serve to purify the atmosphere, and thus execute in the Antarctic latitudes the office of the trees and grasses of the temperate regions, and the broad foliage of the palms of the tropics."

Dr. Hooker also remarks that the siliceous envelopes of the same kinds of diatomaceæ now living in the waters of the South Polar Ocean, have contributed in past ages to the formation of European strata; for the tripoli and the phonolite stones of the Rhine, contain the siliceous envelopes of identical species.

Such are the comments of one of our most distinguished botanists, on the phenomena under review. The reader will perhaps ask, what then are the essential characters which separate the animal from the vegetable kingdom? To this question it is impossible to give a satisfactory reply: perhaps the only distinction that will be generally admitted by zoologists and botanists is the following:—animals requireorganic substances for their support; vegetables derive their sustenance from inorganic matter.

RECENT DIATOMACEÆ.

Recent Diatomaceæ.Plate IV.—To familiarize the reader with the nature of these vegetable organisms, a few recent species are represented in Plate IV., coloured as they appear when alive, under the microscope; the figures are magnified as expressed by the fractions.

Xanthidium.Plate IV. figs. 1, 2, 3, 4, 5.—The case or frustule of this genus consists of a hollow, siliceous globe, beset with spines. The increase of the Xanthidia by self-division, produces the double appearance in the figures, all of which are in the progress of separation.[63]

[63]The organisms so abundant in the flint and chalk, and which were referred by M. Ehrenberg to this genus, and consequently described under the name of Xanthidia by myself and others, are certainly in nowise related to the recent forms: they are flexible envelopes, and probably belong to zoophytes; as will be shown in the sequel.

Pyxidiculum.Plate IV. fig. 2.—The case is a little saucer-shaped box, and is invested by a membrane.

Bacillaria.Plate IV. fig. 6.—A simple siliceous frustule, of a prismatic shape, forming a brilliant chain, which often appears in zigzag, in consequence of incomplete self-division. An immense number and variety of forms are placed in this family by Ehrenberg, with a multitude of generic and specific names. The fresh-water species inhabit every pond and lake, and the marine every sea. Fossil species are equally abundant.

Cocconeis.Plate IV. fig. 7.—This is a very elegant type; the frustule consists of a simple siliceous case, with a central opening; it never occurs in chains like the former. It has been found fossil near Cassel.

Navicula.Plate IV. figs. 8, 9, 14, 15.—The plants of this genus are free, and float in the water apparently by the agency of cilia. Their case is a boat-like envelope with sixopenings, composed of pure silex, and in many species is exquisitely ornamented. Figs. 8 and 9. show a livingNavicula, viewed in front, and in profile: infig.9 are represented the currents produced when the body is moving through the water; after Ehrenberg. FossilNaviculæabound in many tertiary strata.

Galionella.Plate IV. figs. 10, 11.—These algæ are free, and the frustules of a cylindrical, globular, or discoidal form; they occur in chains, in consequence of the self-division being imperfect, and the new individuals remaining attached to the old. TheGalionellæare most abundant and prolific, and inhabit every pool, stream, and lake: fossil species occur in the Virginian marls, and other strata.

Synhedra.Plate IV. fig. 12.—The frustules are siliceous, and of a slender, elongated form. The plant is attached by the base (fig. 12 a.) in youth, and afterwards becomes free. It is found fossil in the Mountain-meal of Santa Flora, and many other deposits.

Podosphenia.Plate IV. fig. 13.—The frustule is cruciform, or wedge-shaped, and attached in youth by the small end, but afterwards becomes free. These plants are often arranged in clusters, as in the figure. M. Ehrenberg states that they inhabit the sea, and not fresh-water; but I have found them in streams communicating with the Thames.Podospheniæabound in the polishing slate of Bilin.

Eunotia.Plate IV. figs. 16, 17.—The frustule is siliceous, and either simple or bivalve; flat below, and convex, and often richly dentated above. An empty case is shownfig. 16; and a group of livingEunoticeattached to a stem of conferva,fig. 17. Several fossil species have been discovered at Santa Flora.

That the general reader, whose attention is for the first time directed to this subject, may be prepared for the enormousdeposits of fossil diatomaceæ that are found in some formations, I subjoin the observations of Dr. Bailey on an elegant fragile species, which hangs together in clusters, appearing like spiral chains, and is about1/20of a line in diameter; it is namedMeridion vernale.

"This fresh-water plant is seen in immense quantities in the mountain brooks around West Point, the bottoms of which are literally covered in the first warm days of spring with a ferruginous-coloured mucous matter, about a quarter of an inch thick, that, on examination by the microscope, proves to be filled with millions and millions of these exquisitely beautiful siliceous organisms. Every submerged stone, twig, and spear of grass, is enveloped by them; and the waving plume-like appearance of a filamentous body covered in this manner, is often extremely elegant. Alcohol completely dissolves the endochrome (soft colouring matter) of this species, and the frustules are left as colourless as glass, and resist the action of fire."[64]

[64]Trans. Amer. Assoc. Geolog. 1843, p. 152.

The yellow or ochreous scum observable in ponds, ditches, and stagnant pools, is an aggregation of diatomaceæ, whose frustules are feriniginous, and of such extreme minuteness, that a billion of their cases would not be more than a cubic inch in bulk.[65]

[65]Ehrenberg.

Fossil Diatomaceæ.—From this notice of a few recent types, we proceed to the investigation of the fossil remains of this tribe of Algæ.

In peat-bogs and swamps, both of modern and ancient date, masses of a white marly or siliceous paste (hydrate of silica), are often observed, and these are found upon microscopical observation to be wholly made up of the frustules ofNaviculæ,Bacillariæ,Galionellæ, &c., with an intermixture of the needle-like spicules of fresh-water sponges. Many of the peat-bogs of Ireland contain layers of a whiteearthy substance, which, when dry, is of the appearance and consistence of friable chalk, and entirely consists of the siliceous cases of various kinds of diatomaceæ.

Lign. 4. Siliceous Frustules of Diatomaceæ, and Spicules of Spongillæ;from a deposit on the banks of the river Bann, Ireland.(Seen by transmitted light, and highly magnified.)

FOSSIL DIATOMACEÆ OF IRELAND.

Fossil Diatomaceæ from Ireland,Lign.4.—Dr. Drummond describes a bed of this kind near the base of the Mourne Mountains, in the County of Down, Ireland. It consists of a very light white substance, resembling in appearance carbonate of magnesia: it has a coarse and somewhat fibrous fracture, and is easily reduced to powder. It is almost entirely siliceous, and is composed of the cases of diatomaceæ of the usual fresh-water species, without any admixture of inorganic matter.[66]

[66]Mag. Nat. Hist. New Series, vol. iii. p. 353, July 1839.

On the banks of the river Bann, in the same county, there is an extensive stratum of a similar earth, and which, from being in much request for polishing plate, is locally known as Lord Roden's plate powder. This earth is wholly made up of the siliceous frustules of many kinds of this tribeof Algæ, and a few grains under the microscope yield a great variety of exquisite forms: figures of several are given inLign.4, from specimens of this earth, with which I was favoured by the Countess of Caledon. They comprise two or three species of Navicula, Galionella, Coscinodiscus, Gomphonema, Bacillaria, Stauroneis, &c., and spicules or spines of fresh-water sponges.[67]

[67]The names of the usual kinds of Diatomaceous frustules may be learnt by reference to Mr. Andrew Pritchard's abstract (with coloured figures) of Ehrenberg's Infusoria. The splendid work of Mr. Ralfs, on the British Desmidieæ, 1 vol. 4to, with coloured plates, is the best guide for those who wish to study the recent plants.

Beds of siliceous marl—that is, of argillaceous earth combined with a large amount of minute particles of silex, all of which prove to be organisms when examined by a high magnifying power,—have been found in numerous places not only in England, but all over the world, since M. Ehrenberg first directed attention to their nature and origin.

Near Bryansford (Newcastle), Binstwick in Holderness, and in the Fens of Lincolnshire and Cambridgeshire, extensive fresh-water microphytal deposits have been discovered and examined.

From our Antipodes I have received many examples of these vegetable earths. My eldest son, Mr. Walter Mantell, discovered an extensive bed of white marl on the banks of the great brackish-water lake of Waihora, in the middle island of New Zealand, consisting entirely of frustules of Bacillariæ. From New Plymouth he obtained some new and exquisite forms of Navicula, Stauroneis, &c.; ranges of low hillocks of sand, of considerable extent, being made up of microphytes (microscopic plants).[68]

[68]See a Memoir on the Geology and Fossil Remains of New Zealand, from the researches of Walter Mantell, Esq.—Geol. Journal, vol. vi.pl.29.

Mr. Dean, of Clapham Common, informs me that alarge quantity of white earth sent from New Zealand as native magnesia, he found to consist wholly of frustules of diatomaceæ, chiefly ofGalionellæ. (SeeLign. 5.)

Lign. 5.Fossil. Galiomellæ;highly magnified.

In America, recent beds of this kind of great extent have been observed and examined by that distinguished microscopist, Dr. Bailey, Professor of Chemistry in the Military Academy at West Point: and the pages of that excellent scientific periodical, Silliman'sAmerican Journal of Science, are enriched with figures and descriptions of the microphytes of which they are mainly composed.

But the Tertiary formations contain strata of this nature, which far surpass in the abundance and variety of their organic contents, any of the modern deposits we have noticed. ThePolierschiefer, orpolishing-slateof Bilin, is stated, by M. Ehrenberg, to form a series of strata fourteen feet in thickness, entirely made up of the siliceous shells ofGalionellæ, of such extreme minuteness, that a cubic inch of the stone contains forty-one thousand millions. TheBerghmehl(mountain-meal, orfossil farina), of San Flora, in Tuscany, is one mass of these organisms.

In Lapland a similar earth is met with, which, in times of scarcity, is mixed by the inhabitants with the ground bark of trees, for food; some of this earth was found to contain twenty different species of algæ.

In the district of Soos, near Egra, in Bohemia, a fine white infusorial earth occurs, about three feet beneath the surface; this substance, when dried, appears to the naked eve like pure magnesia, but under the microscope is seen to be mainly constituted of elegant disciform cases of aspecies ofCampilodiscus, of which figures are given,Lign. 111, figs. 1, 2.

Some beds of porcelain-earth M. Ehrenberg found to be in a great measure made up of concentric articulated rings, entire and in fragments (seeLign. 6), which he believes to be bacillariæ.

FOSSIL DIATOMACEÆ OF VIRGINIA.

Lign. 6 Organic Bodies in Porcelain Earth;highly magnified.

Fossil Diatomaceæ of the Richmond-earth; Virginia.—The town of Richmond, in Virginia, is built on strata of siliceous marl of great extent, which earth; highly magnified. have a total thickness, beneath and around the town, of more than twenty feet. These marls, whose organic composition was first detected by Professor W. B. Rogers, are referred by that eminent American geologist, to the older tertiary (eocene, ormiocene) formations. They occupy considerable districts, spreading out into sterile tracts along the flanks of the hills, their siliceous character rendering them unfavourable to vegetation. The investigations of Dr. Bailey have shown that the frustules so abundant in this earth, consist of several species of Navicula (Lign. 1, fig. 1, 1a.), Galionella (Lign. 1. fig. 3, 3a.),Actinocyclus(Lign. 1, figs. 4, 5), &c.

The most remarkable forms are disciform frustules, having their surfaces elaborately ornamented with hexagonal spots disposed in curves, and bearing some resemblance to the engine-turned case of a watch.Lign. 7, fig. 2, is a small segment of a disc, very highly magnified. These frustules vary in size from1/100to1/1000of an inch in diameter; they are namedCoscinodiscus(sieve-like disc), and there are several species: one less richly sculptured,C. patina, is figuredLign. 7, fig. 6. Circular bodies, with five or six lines radiating from the centre to the circumference, like thespokes of a wheel, hence namedActinocyclus(Lign. 7, figs. 4, 5), and spicules of Sponges, are also abundant.

Lign. 7. Microphytes[69]from the Richmond-earth;highly magnified.Tertiary. Virginia.Fig.1.—Navicula. 1a. Side view.2.—Coscinodiscus radiatus; a portion of the circular shield.3.—Galionella sulcata; the upper figure shows the transverse face of one of the frustules.3a.—Three united cells viewed laterally.4, 5.—Actinocyclus.Two species.6.—Coscinodiscus patina; transverse view. 6a. Lateral view.

[69]As the termInfusorial-earthmust be abandoned, it will be convenient to substitute a name simply expressive of the nature of the most abundant organisms that enter into the composition of these deposits: that ofMicrophyta, orMicrophytes, (from μικρος,mikros, small, and φυτον,phyton, a plant), signifying very minute vegetables, may perhaps be admissible: in this sense the word microphytal is employed in these pages.

When a few grains of the marl are prepared, and mounted on a glass, almost all these varieties will be manifest, so largely is this earth composed of organic structures; in fact, very few inorganic particles are intermixed, the merestpellicle left by the evaporation of a drop of water in which some of the marl has been mixed, teeming with the most beautiful structures.

At Petersburg, in Virginia, a sandy marl occurs, interstratified with deposits which, from their shells, are referred to the older tertiary formations. Probably this marl is a continuation of that of Richmond, but it is full of many new forms, associated with those common in the earth of the latter locality.[70]

[70]Dr. Bailey, with great liberality, has so amply supplied myself and other observers with specimens of these deposits for examination, that the fossils above described are familiar to all British microscopists. Figures of many of those organisms are given in the American Journal of Science.

It is an interesting fact, (first observed by Mr. Hamlin Lee,) that the common Scallop (Pecten maximus), as well as the Barnacle (Balanus), feed on diatomaceæ, and their stomachs generally contain numerous cases of Coscinodisci, Dichtyochi, Actinocycli, &c.: a slide prepared and mounted with the contents of the stomachs of these mollusks, presents an assemblage of forms identical with those found in the tertiary earths of Virginia.[71]

[71]See my "Thoughts on Animalcules," p. 103.

In the mud of the quicksands on the shore at Brighton, Mr. Reginald Mantell found recent Coscinodisci, &c. associated with fossil polythalamia that had been washed out of the chalk, and precipitated with the frustules of the recent diatomaceæ, into the sediments now in progress.

The prevalence of marine and fresh-water forms in the same deposit is not unusual; and the remarks of Dr. Bailey on this fact are so pertinent, that I insert them, as a salutary caution against hasty generalizations on subjects connected with these investigations. After describing a species of Galionella (G. moniliformis), as an inhabitant only of salt and brackish water, and stating that he had alsofound it sixty miles up the Hudson River, near West Point, Dr. Bailey observes—"The Fauna and Flora of the Hudson at this place would, if in a fossil state, be rather puzzling to the geologist, on account of the singular mixture of marine and fluviatile species. WhileValisneriaandPotamogeton(two common fresh-water plants), grow in such vast quantities, in some places, as to prevent the passage of a boat, and the shore is strewn with fluviatile shells (such as Planorbis, Physa, &c.) in a living state, yet the above plants are entangled with Algæ (sea-weeds), and marine parasitic zoophytes; while the rocks below low-water mark are covered with Balani (barnacles) and minute corallines, and the marine Flora is represented by vast quantities of very elegant sea plants."[72]

[72]American Journal of Science, vol. x. p. 41.

I must here close this extended notice of the fossil remains of a class of vegetable organisms, which, though for the most part invisible to the unassisted eye as individual forms, constitute by their inconceivable multitudes an important element in the formation of sedimentary deposits. The fact of their having been formerly treated of as animalcules, and generally regarded as belonging to the animal kingdom, rendered a full consideration of the phenomena necessary, in order to place the subject before the reader in a clear and comprehensive point of view.[73]

[73]As both the recent and fossil frustules of Diatomaceæ are beautiful objects for the microscope and polariscope, they are in much request. Specimens mounted on glass slides may be had of Mr. Topping, and Mr. Poulton. See Appendix.

Confervites.—The cellular aquatic plants named Confervæ are sometimes found in transparent quartz pebbles, and in chalk, appearing as delicate simple or branched filaments, which, by the aid of the microscope, are seen to bearticulated. Seven species are described by authors, but the vegetable nature of some of these is doubtful. A beautiful species in Chalk, first noticed by the late Samuel Woodward, Esq. (author of the Geology of Norfolk), is here figured.

Lign. 8. Confervites Woodwardii;nat.Chalk. Norfolk.

FOSSIL FUCOIDS.

Fossil Fucoids.—Of the tribe of Algæ which comprises the sea-weeds that are not articulated, many fossil species occur in very ancient, as well as in modern, fossiliferous deposits. In the Lower Silurian rocks of North America, beds of limestone of great extent are full of a large digitated Fucus (Fucoides Alleghaniensis).[74]The Firestone or Malm-rock of Bignor in Sussex abounds in a ramose variety (Fucoides Targionii,Vég. Foss.p. 56), of which specimens are figured in the vignette of this volume, and inLign. 9.

[74]Figured and described in Dr. Harlan's Medical and Physical Researches: Philadelphia, 1835, p. 393.

Chondrites.—These fossil algæ approach nearest to the living species ofChondrus(hence the name of the genus). The frond is thick, branched, dichotomous, with cylindricalor claviform divisions, with a smooth surface and without tubercles. The substance of the Bignor fossils is a white friable earth, which strikingly contrasts with the dark grey malm-rock that forms the matrix. As the Sussex Chalk Chondrites appear to be distinct from the Tertiary species named by M. BrongniartC. Targionii, I have, at the suggestion of Mr. Morris, substitutedC. Bignoriensis, to indicate the locality in Sussex in which I discovered it forty years since. In the chalk-flints ramose fuci occasionally occur, but not in a state of preservation that admits of the determination of the forms of the originals.

Lign. 9.Chondrites Bignoriensis;nat.Malm-rock. Bignor, Sussex.

The tertiary marls and limestones of Monte Bolca yield several beautiful species of Algæ, one of which is figured inLign. 10. It is referred to the fossil genusDelesserites(Sternberg), which includes those algæ that have thin, and flat or undulated, smooth, membranous fronds, with a median rib.

Of the little plants comprised in the class of cellular cryptogamia, which have stems, leaves, and fructification, but no true vessels, two or three species of Moss and Liverwort have been met with in tertiary strata. Mosses as well as Fuci are occasionally imbedded in quartz pebbles, in which they appear of their natural colour, and apparently floating in the transparent medium. A beautiful green moss, with a Conferva twined round its base, is figuredLign. 11, p. 104, from a specimen described by the late Dr. Macculloch. It is supposed to be related toHypnum(Geol. Trans.vol. ii.).

MOCHA-STONES.

Moss-agates and Mocha-stones.—The beautiful siliceous pebbles called Moss-agates, and Mocha-stones, will so often come under the notice of the collector, that, although but extremely few, if any, of these objects contain organic remains, the arborescent substances they inclose being merely metallic oxides, a few remarks on their nature may be expected. The late Dr. Macculloch paid considerable attention to the investigation of these bodies, and believed that some of the objects imbedded in the pure and compact quartz were really of vegetable or animal origin; the specimen figuredLign. 11is of this kind; the fossils being apparently cellular cryptogamous plants. InGeol. Trans, vol. ii., other examples are figured and described by the same sagacious observer. Mr. Bowerbank is of opinion that spongeous structure enters into the composition of almost all the moss-agates, and I have no doubt that in some instances such organisms are present: but in by far the greater number of agates and mocha-stones the inclosed bodies are mere crystallizations; they are arborescent or dendritical oxides of manganese, copper, chlorite, iron, &c.

Lign. 10 Delesserites (Fucoides) Lamourouxii.Monte Bolca.(Vég. Foss. Br.)

Lign. 11.Moss and Conferva,in transparent quartz, × 3.

M. Brongniart, who carefully examined a great number of agates and pebbles, with the view of determining if vegetable substances were ever imbedded in them, could not detect a single instance in which the apparent mosses, confervæ, or algæ, were organic; in every case the mineral origin of the pseudo-vegetation was, in his opinion, unequivocal. Some of the beautiful green arborescent bodies in quartz pebbles, even under the microscope, present so close a resemblance to confervæ and mosses, that it is difficult to persuade oneself they are not vegetable structures; but the observations of M. Brongniart appear to me conclusive as to their mineral nature.[75]With the exception of three or four species ofJungermannia, and four or five ofMuscitesin Amber, M. Brongniart states that he knows but one true fossil plant of the family of Mosses; theMuscites Tournaliifrom the fresh-water tertiary deposits of Armissan.

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