This fact of degradation, strangely indicated in geologic history, with reference to all the greater divisions of the animal kingdom, has often appeared to me a surpassingly wonderful one. We can see but imperfectly, in those twilight depths to which all such subjects necessarily belong; and yet at times enough does appear to show us what a very superficial thing infidelity may be. The general advance in creation has been incalculably great. The lower divisions of the vertebrata preceded the higher;—the fish preceded the reptile, the reptile preceded the bird, the bird preceded the mammiferous quadruped, and the mammiferous quadruped preceded man. And yet, is there one of these great divisions in which, in at least some prominent feature, the present, through this mysterious element of degradation, is not inferior to the past? There was a time in which the ichthyic form constituted the highest example of life; but the seas during that period did not swarm with fish of the degraded type. There was, in like manner, a time when all the carnivora and all the herbivorous quadrupeds were represented by reptiles; but there are no such magnificent reptiles on the earth now as reigned over it then. There was an after time, when birds seem to have been the sole representatives of the warm-blooded animals; but we find, from the prints of their feet left in sandstone, that the tallest men might have “Walked under their huge legs, and peeped about.” Further, there was an age when the quadrupedal mammals were the magnates of creation; but it was an age in which the sagacious elephant, now extinct, save in the comparatively small Asiatic and African circles, and restricted to two species, was the inhabitant of every country of the Old World, from its southern extremity to the frozen shores of the northern ocean; and when vast herds of a closely allied and equally colossal genus occupied its place in the New. And now, in the times of the high-placed human dynasty,—of those formally delegated monarchs of creation, whose nature it is to look behind them upon the past, and before them, with mingled fear and hope, upon the future,—do we not as certainly see the elements of a state of ever-sinking degradation, which is to exist for ever, as of a state of ever-increasing perfectibility, to which there is to be no end? Nay, of a higher race, of which we know but little, this much we at least know, that they long since separated into two great classes,—that of the “elect angels,” and of “angels, that kept not their first estate.” EVIDENCE OF THE SILURIAN MOLLUSCS—OF THE FOSSIL FLORA. ANCIENT TREE.