The fifth class is characterized by the prevalence of common roofing and writing slates. The sixth and lowest by that of some finer vareities of slate and granite."

These classes have been differently modified by other writers; the arrangement here given, is that which our authors consider the most convenient to the student and most conformable with nature.

With respect to the names given to the different formations, a wide difference obtains between different geological schools. Different parties have given names borrowed from their peculiar theoretical views, and often conveying descriptive ideas, which are far from being universally applicable in order to avoid these objections, the authors of the present work have adopted names implying nothing more than the unquestionable facts of the relative positions of the formations. Regarding the third, or carboniferous series as the middle group, they have assigned the term supermedial to the second series, as being next above it, and submedial to the fourth, as being next below it. To the highest and lowest series the terms superior and inferior, which require no commentary, have been applied.

The most general relation under which the various formations present themselves, is that whence they have been denominated primitive and secondary. The former class comprises those rocks, which from the consideration of superposition, are the lowest, and form a sort of base, if that term may be applied to the greatest elevations of the earth's surface, around which, or against which, the various superior strata repose. From the circumstance of these rocks never containing any organic remains, and being of a simple chemical composition, it was inferred that they constituted the sole materials of the earth's surface at the time of its first formation; and were therefore denominated primitive: in the work before us they are simply called rocks of the inferior order.

In all the rocks above these, more or less, we find the imbedded and mineralized remains of animal and vegetable bodies. We observe them also in many instances composed of fragments evidently torn by some great convulsions of nature from the former class, and cemented together again under a new form. Hence, therefore, a line of distinction was drawn, and the secondary and subsequent origin of all such rocks being clearly deducible from the appearances they presented, they thence received their designation. This designation is, however, insufficient without

further subdivisions, since a class of rocks was soon re cognized, bearing a close resemblance to the structure and chemical composition of the primary, and containing very few organic remains: to these the title of transition rocks was given by Werner. To distinguish the rest of the secondary class, the term flatz was introduced by the same celebrated geologist, significative of their comparatively flat and horizontal arrangement. This name, however, is greatly misapplied in the case of many rocks of this class, which are nearly as much inclined as the former. Subsequent discoveries made it necessary to distinguish the older from the newer floetz formations. Other geologists seeing the objections to this nomenclature, called the transition rocks of Werner, the intermediate class; the floetz, the secondary; and the newest floetz, the tertiary. This last corresponds with the first, or superior order, according to the enumeration of our authors above given. The correspondence of the rest will be sufficiently obvious. A synoptical view of the different arrangements is given in p. 7.

After observing the order in which the different rocks are arranged, the next object to which the attention is directed is the disposition of the materials of which they are composed; and in this enquiry one of the most curious and interesting points consists in the different sorts of organic remains which are found invariably to accompany and characterize the different formations.

"Thus," as our authors justly observe," there is opened to the view of the student a far more extensive and interesting field of enquiry with regard to the relations of these rocks to the general revolutions of nature; for he will have found in many of these beds spoils of the vegetable and animal kingdom imbedded, particularly the remains of marine zoophytes and shells, and often in such abundance as to constitute nearly the entire mass of particular strata. If he is led by the interest thus excited to examine more closely the phænomena attending the distribution of these remains, he will find them as remarkable in the detail as they are striking in a general point of view. In some countries he will perceive that none of these remains occur (for instance in Cornwall and the Scotch highlands) in others (as in the south eastern counties of England) not a well can be sunk, or pit opened without presenting them in abundance: and pursuing the enquiry, he will arrive at the conclusion, that the lowest series of rocks which have therefore been considered as primitive, are entirely destitute of those remains; that the next contains them sparingly ; while they abound in the three succeeding series, although not without the occasional interposition of beds in which they are still rare, if not altogether wanting."

When these interesting remains are examined by the help of that knowledge which the researches of botany and zoology open to us, their genera and species may be determined; but here the most curious circumstance is, that not only a great part of the species so distinguished, but even whole genera are entirely different from any now known to exist. An objection to this opinion very naturally arises from the consideration that with a large portion of the land, and all the recesses of the ocean, and their organized productions we are altogether unacquainted, and that it is therefore presumptuous to say that certain genera or species do not exist. This objection is fully examined in a note, p. 9. into the details of which we cannot now enter; but it is satisfactorily shewn that we may very safely adopt the conclusion, that a large portion of the fossil animals and plants belonged to a system of beings in many respects widely different from those now inhabiting the earth. Hence it is that

"Geology presents to the comparative anatomist and botanist, but particularly to the former a rich fund of new materials, and adds to the several departments of natural history, supplements, the knowledge of which is indispensable to complete our views of them indeed, in many instances, important peculiarities of organization, and remarkable links in the chain of animated beings are presented in these fossil remains, and many chasms which must otherwise have existed, are filled up in a satisfactory manner."

The chief concern, however, of the geologist in respect to these fossil remains consists in observing the laws by which their association with particular strata is regulated. Observation has detected the constant recurrence of the same species of remains in the same strata. Wherever they occur particular species and genera are confined to particular formations. This general truth is well exemplified by the authors of the work before us :

"It will serve to exemplify the laws which have been stated, if the observer's attention is directed to two of the most prominent formations of this island; namely, the chalk, and the limestone which underlies the coal in Northumberland, Derbyshire, South Wales, and Somerset. Now if he examines a collection of fossils from the chalk of Flamborough Head, or from that of Dover Cliffs, or it may be added, from Poland or Paris, he will find eight or nine species out of ten the same: he will observe the same echinites associated with the same shells: nearly half these echinites he will perceive belong to divisions of that family, unknown in a recent state, and indeed in any other fossil bed except the chalk. If he next proceeds to inspect parcels of fossils from the carbonife

rous limestone, from whichever of the above localities they may have been brought, he will find them to agree in the same manner with each other; that is, he will find the same corals, the same encrinites, the same productæ, terebratulæ, spiriferæ, &c. but if he lastly compares the collection from the chalk with that from the mountain-lime, he will not find one single instance of specific agreement, and in very few instances any thing that would even deceive an unpractised eye by the superficial resemblance of such an agreement."

'The subject of organic remains is certainly one of the most curious which is presented to the notice of the geological student in any part of his researches. It offers for examination some of the most important questions respecting the formation of the present surface of our planet. We. have in the first instance a foundation composed of primitive rocks, granite, gneiss, &c. entirely destitute of such remains. In the next or submedial class, we find corals, encrinites, and testacea, but of different sorts from any now known, and these but sparingly occur. The limestones belonging to the medial class, contain nearly the same species, but more plentifully. The coal measures, however, scarcely present a single shell or coral; but on the contrary, abound with vegetable remains, ferns, flags, reeds of unknown species, and large trunks of succulent plants, strangers to the present globe. Upon the coal, in the next or supermedial class, rest beds again containing marine remains (the mag nesian limestone): after this the formation of new red sandstone presents a long interval, destitute almost entirely of organic remains, and seeming to prepare the way, as it were, for a new order of things. This commences in the lias, and is continued through the succeeding formations, up to the chalk. All these beds contain corals, encrinites, echinites, testaceæ, crustacæ, vertebral fishes, and marine oviparous quadrupeds; all these, however, are widely distinguished from the families contained in the lower beds of the series. They are also particularly characterized and distinguished among themselves, according to the particular stratum in the general class, which they occupy. Thus far the remains are always found petrified, by which term is understood that they are impregnated with the mineral substance in which they are imbedded. In the strata above the chalk, on the contrary, we find the shells themselves preserved, so that when taken out of the substance in which they are imbedded, if it were not for a slight alteration of colour and brittle texture they might be taken for recent specimens. In some parts of these strata we find beds of marine shells, alternating with

others peculiar to fresh water: so that they seem to have been deposited by reciprocating inundations of fresh and salt water. In the highest or most recent beds of this formation we at length find an identity of the fossil species with those now existing. Over all these beds there is spread indiscriminately a covering of gravel, which we cannot but conjecture to have been formed by the rolling and attrition of fragments of different rocks, by the action of water. The length of time, as well as the local extent to which it operated, must have been very considerable to produce such well rounded forms as we observe in the common pebbles, and this over such large portions of the earth's surface; but in these deposits it is more to our immediate subject to notice the conclusion of the great series of organic remains, in the numerous relics of land quadrupeds. Many of them are of unknown genera or species; such for example as the mastodon, the fossil species of the elephant, called mammoth, and other animals. These, however, are mixed with many known species; some not now inhabiting the same regions; such as the hyena, &c.; but many easily identified with those now found in the same parts of the earth.

Besides the remains of organized beings, we find in the secondary strata a different class of substances imbedded, and from an attentive consideration of which much light may be thrown on the convulsions of nature, by which those rocks in their present state must have been formed. These are the fragments of older rocks, rounded by the attrition produced by the action of water. Thus we find the lower strata of the supermedial order, containing in great abundance rolled fragments of the carboniferous limestone, be longing to the class next below, as well of many still older rocks. The beds particularly alluded to, are what are called the conglomerate rocks of the new red sandstone; they are in fact little more than a consolidated mass of the debris of those rocks which, in position, form the basis› against which they rest, and by the very circumstance of the occurrence of these fragments, are proved (if further proof be wanting,) to be of much older date. These arguments are given at large in the work before us. Without entering further upon them, we will proceed to another circumstance, which is the occurrence of marine remains in formations occupying large portions of our continents, and even the summits of our loftiest mountains. Hence it seems an inevitable consequence, that the greater part of these continents have not only been covered by, but formed of materials collected from the bottom of the ocean. Hence VOL. XX. SEPT. 1823.

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