In the oldest of the sedimentary rocks, the remains of animals occur in vast numbers; nor will any one, I trust, of ordinary intelligence, doubt but these relics once constituted living beings. Through the whole series of rocks, six miles in thickness, we find similar remains, even increasing in numbers as we ascend; but it is not till we reach the very highest stratum, the mere superficial coat of alluvium, that we find the remains of man. The vast multitudes, then, of organized beings that lie entombed in rocks below alluvium, must have yielded to death long before man received his sentence, _Dust thou art, and to dust shalt thou return._ Will any one maintain that none of these animals preceded man in the period of their existence? Then why are the remains of men not found with theirs? for his bony skeleton is as likely to be preserved and petrified as theirs. Moreover, so unlike to man and other existing tenants of the globe are many of these ancient animals, that the sure laws of comparative anatomy show us, that both races could not live and flourish in a world adapted to the one or the other. If the temperature had been warm enough for the fossil tribes, and all the circumstances of food and climate congenial to their natures, they would have been unsuited to the present races; and if adapted to the latter, the former must have perished. The difference between the animals and plants dug out of the rocks in this latitude, and those now inhabiting the same region of country, is certainly as great as that between the animals and plants of the torrid and temperate zones; in most cases it is greater. Now, suppose that the animals and plants of the temperate zones were to change places with those between the tropics. A few species might survive, but the greater part would be destroyed. Hence, _a fortiori_, had the living beings now entombed in the rocks been placed in the same climate with those now alive upon the globe, the like result would have followed. I say _a fortiori_; that is, for a stronger reason, the greater number must have perished; and the stronger reason is, the greater difference between fossil and living species, than between the latter in torrid and temperate latitudes. It is true that man is among the species capable of being acclimated to great extremes. And yet no physiologist will imagine that even his nature could have long survived in such a climate as formerly existed, when probably the atmosphere was loaded with carbonic acid and other mephitic gases, and with moisture and miasms, the result of a rank vegetation, and of a temperature higher than now exists in equatorial countries.