LETTER XVIII.

ON THE FOSSIL REMAINS OF ANIMALS FOUND IN THE ROCKS AND STRATA OF THE EARTH.-I. THOSE IN THE SECONDARY STRATA OF THE MARINE CLASSES.-II. THE LAND-QUADRUPEDS OF THE TERTIARY BEDS.-NOTHING INCONSISTENT WITH THE MOSAIC COSMOGONY.

MY DEAR SON,

THE other topics which remain to complete my objects in these letters will not allow me to detail to you all the facts that ought to be known and considered with respect to the fossil remains of animals which the rocks and strata of our earth contain, and which human labor or curiosity has disclosed, in modern times, to our view. To do full justice to the subject, the right theory of our geology ought to be first well settled. But the diversities of opinion which still prevail, show that this is impossible at present. We know enough for ingenious speculation, and also for hesitation and doubt; and we are from time to time acquiring more elucidating knowledge, which is leading the intelligent inquirers, who are pursuing this interesting subject, to better reasoning, and to more just conclusions. But we seem to have arrived at that point in which further discoveries from our mineralogical investigations become necessary, before any true system can be established as to the formation of our globe. Scientific men have traced its constituent substances to sixty or more simpler bodies, which at present rank as elements, because they are not yet further decomposable; and these appear to have constituted our primordial rocks. But there are abundant reasons for surmising that they are not the primitive elements of material nature; and therefore until they can be resolved into the particles or substances which are so, we shall not attain those perceptions of the original composition of our multifarious earth, which will present the deciding and satisfactory truth. We must

know what silica, alumina, magnesia, lime, carbon, iron, and the other metals and primitive components of the minerals intrinsically are, before we can accurately discern the process of the succession, the causations, the agencies, the laws, and the principles, on which the primary and secondary masses were originally formed. The acquisition of this further information would have been thought impossible in the last century. But human sagacity and industry are now exploring what is unknown, so perseveringly and so successfully that every month may bring us the information, that some diligent analyst, in some country or other, may be drawing from nature those great secrets of her primordial chemistry, which have hitherto been impervious and inaccessible. In this state of unsatisfactory ignorance and uncertainty, it will be sufficient to notice the organic remains which have been disclosed, with a few brief remarks on the subterraneous structure which contains them.

The ground we tread upon, and from which vegetation now springs, is not the primitive surface of the earth. It is the upper part of the last series of strata which have been deposited upon and around it, and which is now most commonly denominated the TERTIARY formations. By this term, the series of subterraneous beds, down to the chalk rocks, are named and known; and they are manifestly more recent than the masses below them.(1) These are considered by many, and, I think, justly, to have been formed at the period of the deluge, from the fragments and ruins of the earth's previous surface, amid the concussions and perturbations of that general catastrophe.(2) But, however this be, these tertiary beds are clearly distinguishable from the more ancient, and are treated of as a class by

(1) Conyb. Geol. Introd. v.-vii. M. de Serres Geogn. p. xcii. (2) M. Dufresnoy calls the beds that have been deposited on the extensive chalk formation "terrains tertianes." Bull. Un. 1831, No. 4, p. 38.

"We find a mantle, as it were, of earth and sand indifferently covering all the solid strata, and evidently derived from some convulsion which has lacerated and partially broken up those strata, inasmuch as its materials are demonstratively fragments of the subjacent rocks, rounded by attrition." "Hence they must be assigned to the last violent and general catastrophe which the earth's surface has undergone." Mr. Conybeare, therefore, calls them diluvial. Out. Geol. p. 4.

themselves, different from what preceded them in position, appearance, fossils, and composition.(3)

Below these occur another great series of various rocks, of a stratified and cedimentary nature, which have been called transition, or intermediary, and upper and lower secondary.(4) But to all these, the general term, secondary, as marking one great outline of chronological distinction, from both the earlier and the later, and as embracing the whole series, seems to be very fitly applicable.(5) This leaves that of primary, or primordial, for those crystaline and other masses which are found beneath them, and on which they rest, and beyond which human knowledge has not penetrated. These are, the granite, gneiss, and mica slate rocks, with their subordinate resemblances.(6) All these are mainly formed of the same materials, in different proportions and modifications; quartz, felspar, and mica, with some occasional additions of a few other particles; and they are found in all regions of the globe, and of the same composition.(7)

In these primordial rocks no organic remains have been seen; and from this circumstance it is reasonably and generally concluded that they were formed before animal or vegetable life began. It is in the secondary rocks, those that were deposited or composed after the primary ones

(3) M. Marcel de Serres' "Geognosie des Terrains Tertianes," 1829, is devoted to this class of the earth's strata, and to their animal fossils.

(4) "Transition, or intermediate rocks, cover those of the primary class, and are distinguished as the lowest rocks, in which the fossil remains of animals or vegetables are found." Bakewell Geol. p. 124. ... . In these he includes the slate, gray wacke, and mountain limestone. His upper secondary class comprises the magnesian limestone, red sandstone, lias, oolites, sand, clay, and chalk-rocks (p. 236); naming the coal formations his "lower secondary." 146.

(5) M. Marcel de Serres accordingly attaches the denomination of secondary to all these classes, distinguishing them into the three modifications of" upper, middle, and lower." Geog. p. xcii...... This simplicity seems preferable, in a large outline of the subject, to M. Al. Brongniart's numerous minute divisions, with a long train of new Greek-derived names.

(6) Bakewell's Intr. Geol. p. 84, 5. Al. Brongn. Ecorce du Globe, p. 340, 1.

(7) "With the granitoid group all the earth is covered." Al. Brongn. p. 342..... "Geologists have observed, that mountain masses display every where the same rocks; the same assemblage of mica, quartz, and felspar, in granite; of mica, quartz, and garnet, in mica slate; and of felspar and hornblende in syenite." Humboldt's Geogn. Ess. p. 4.

were consolidated, and before the tertiary strata accrued, that fossil exuviæ have occurred.

The SECONDARY formations consist of new rocks, formed from the fragmentary ruins or disintegration of the primordial ones, or from new compounds of their constituent substances, with the addition of various successions of others of the calcareous or limestone classes. The most ancient of these are the argillaceous schist or clay slates, from which our various kinds of slates are derived; the conglomerates, gray wacke, and old red sandstone, the carboniferous or mountain limestone, the coal measures, and their vegetable remains, which we have noticed in a preceding letter. The subsequent rocks above these, of the new red sandstone, the magnesian limestone and red marl, with the calcareous beds of lias and oolites, iron sand, and green sand, follow. Above all these the chalk masses lie, that terminate the series to which the appellation of secondary has been conveniently appropriated.(8)

After these a new state and order of things begin in the tertiary rocks and strata, which are above the chalk beds, and which, in a succession and intermixture of clay, sand, marl, and limestone strata, ascend up to our present inhabited surface. I will not enter into any detail on these, nor on their predecessors. It will be sufficient to have enumerated the whole in this general notice, in order to enable you to understand more satisfactorily to yourself the position and history of the fossil remains, which they have preserved, and now disclose to our knowledge, of some of the former animals of the more ancient period of our earth.

All the animal remains found in any part of the secondary rocks and strata, are of those who inhabited the prime

(8) To this second class of rocks, the valuable volume of Mr. Conybeare and Mr. Philips, in their "Outlines of Geology," is devoted.... The 11th, 12th, and 13th chapters of Mr. Bakewell's sensible work also treat upon them. The plates to his work are pleasing and satisfactory illustrations..... Dr. Ure's second book of his Geology adds much important information; and much accession of matter and thought will be found on the same subject in several chapters of Dr. McCulloch's Geology; and in the "Periode Saturnienne ou Antediluvienne" of M. Al. Brongniart's Tableu. Paris, 1829..... I only regret his new nomenclature, as it is not likely to be generally adopted; and therefore perplexes the study of the science by a disadvantageous quantity of exotic terms, which do not seem to be either necessary or beneficial.

val waters. The great bulk of them are of the testaceous and zoophyte orders, with a few fish. Several of these are species which have now ceased to exist; but they are so analogous to the genera which still inhabit our seas, that they display no remarkable differences from them. These occur first in the clay slate, and abound principally in the mountain or carboniferous limestone. But in the lias of England, remains of the amphibious genera have been discovered, which have no similitude in any species that now appear, and which are really extraordinary, both in their size and figure.(9)

One of the earliest beds after the primordial rocks, and into which mica slate is in some places seen passing, is the CLAY SLATE formation. In this rock, called also argillaceous schist, ichthyolites, or fossil remains of fish, have been found, in Switzerland, in Germany, France, Italy, Dalmatia, and Syria.(10) These antediluvian fish are those of several of our present genera.(11)

In the older LIMESTONES of Flanders, a great quantity of zoophytes have been observed. The madepcres and millepores are abundant. The orthoceratites, which approach to that order of animals, also occur in considerable abundance, along with fragments of entrochi and encrinites.(12)

(9) On the fossils found in England in these secondary strata, Mr. Conybeare's chapters are the most original and satisfactory. The science is much indebted to him, both as a discoverer and as a reasoner. Cuvier takes the lead of all, in his important work on the subject. Dr. Ure has ably brought together some of the most remarkable facts as to the antediluvian animals. And Mr. Parkinson, in his "Organic Remains," and "Outlines of Oryctology," supplies a fund of more particular information, especially as to the testaceous and zoophyte remains.

(10) The article "Poissons Fossiles," in the Dictionnaire des Sciences Naturelles, details these fossils; and Dr. Ure, from that, has specified six localities of them in his Geology. p. 141-6.

(11) "In the famous locality of Monte Bolea (in the Veronese) the following genera are found: the shark, ray, file-fish, sun-fish, globe-fish, palæobalistum, trumpet-fish, pike, lilurus, herring, pipe-fish, cod, blenny, goby, mackarel, bull-head, gurnard, gilt-head, sciana, perch, flounder, amia, fistularia, flying fish, murænophis, eel, dory, and several others." Ure, p. 147.

(12) Dr. Ure, p. 149. “The shells most frequently found there are terebratulites, turbinite, certain ammonites, and belemmites; but the only fossil which appears to be characteristic of the transition limestone, is the trilobite, a singular extinct animal of either the crustaceous or insect tribe." Ib. .... Mr. Bakewell's Geology contains a print of this, of the natural size.