Yet, in accounting for these fossils thus found far remov ed from the sea, the greater number of authors, whether following Tertullian, or drawing from their own resources, have considered them as having been deposited by the deluge; a notion much insisted on, even in later times, by those who ought to have been better informed. We will not dwell on this subject at present, but may remark that it was this argument, probably, which induced Voltaire to deny the' fact altogether as a natural occurrence, and to account for organic fossils by accidental causes. The question is examined in his miscellaneous writings, and also in a letter dated from Italy. But we need not record the opinions of an author so utterly ignorant of the facts, as to think that the shells found on the Alps might have been dropt by pilgrims in their passage homewards from Syria, and that the petrified fishes of Italy, not now to be found in the Mediterrrnean, were fish that had been rejected from the tables of the Romans as unwholesome.
But all these follies are for ever past; and since the time that Rouelle first proved that fossil shells were depo sited in colonies, just as living species are now, that they varied in different places, and that different kinds occupied different strata, this branch of knowledge has made rapid strides towards perfection.
On the Rocks in 'which Organic Remains are found.
Although organic remains are found in'every part of the world, and at various elevations above the surface, even in deed on some of the highest mountains of the globe, they do not occur in all rocks. It is necessary to distinguish those, as this forms an important part of the history of these bodies.
No such substances have ever yet been found in granite, or in gneiss ; nor is it imagined by any sect of geologists that this ever can happen. Those who suppose that these rocks were primitive, or made before the creation of ani mals, must of course adopt that conclusion ; and among those who conceive that granite is of igneous origin, and that gneiss has been also exposed to the strong action of heat, it is plain that the same supposition is equally a mat ter of necessity. We may also add to these the next of the older schistose strata, which have characters more or less perfectly chemical or crystalline ; and thus horn blende schist, quartz rock, micaceous schist, with the con generous substances chlorite and talcose schists, together with diallage rock and serpentine, are excluded from the list of rocks bearing organized bodies.
In the next place, the trap rocks under all their modifi cations, excepting one, are equally excluded. This ought to be a necessary consequence of the origin of these rocks, if,as is now almost universally admitted, they are analogous to volcanic productions in their causes, as they are in ap pearance, or, to state it plainly, are the produce of fusion.
On account of the exception just alluded to, it is necessary to give a list of these rocks ; particularly as some differen ces of opinion have been entertained on this subject, and as the very question of the igneous origin of this tribe is in some measure involved in the truth or fallacy of that supposition. The rocks, then, of this division, from which organic remains are excluded, are, first, all the porphyries and compact felspars, which, from their frequent connec tion with granite and the older rocks especially, seem to be of the most remote origin. After this come all those which are of far more recent date, and which, indeed, with few exceptions, are of more recent origin than the very latest strata that do contain organic remains in great variety and abundance. This in itself is a strong argument in favour of their igneous origin ; as it is otherwise nearly inexpli cable how, when intermixed with the different rocks that abound in the organic substances, and that, in so many in tricate ways, they should alone have been void of them.
These rocks, then, comprise all the greenstones and grcystones, as they are called, under whatever modifica tions of composition or aspect, together with the other crystalline rocks of this cc..mily, as hypersthene rock, augite rock, syenite, and porphyry, together with the compact clinkstones that approximate in character to compact fel spar. Though not quite so crystalline, all the modifica tions of basalt, that vague rock, and all the claystones, of whatever nature, are eqaually deprived of organic remains, as are the amygdaloids, and, we perhaps need scarcely add, pitchstone ; as, we believe, that is invariably found in the form of veins.
There remains, therefore, but one rock of this wide family, and that is sometimes called tufa, and at others trap conglomerate. Now it is not very common to find organic bodies even in these rocks, yet they do sometimes contain fragments of wood, always, however, much altered ; that is, carbonized, or impregnated with bitumen, or fully bitu minized, so as to pass into coal. No instance has yet been adduced of animal remains, or of sea shells contained in the trap conglomerates although, on general principles, there does not appear any good reason why this should not happen. We are indeed aware that some geologists have pretended to find organic bodies, both wood and sea shells, in the trap rocks, and the latter especially in basalt. This, however, is an error ; arising from not discriminating the exact manner in which the fragments of wood lie in the trap masses, in the one instance, and, in the other, from not distinguishing between basalt and certain stratified rocks, much resembling it in appearance, with which it is occasionally in contact.