I. THE ORGANIC REMAINS are scanty as compared with those of the age immediately anterior. The vegetable forms, as yet detected, are new and distinct. The fishes consist of six or seven genera, and about as many different species. And here commences, it is supposed, the singular change in their ossification, for which science can assign no reason, as it cannot detect the least appearance of graduation into the new, for the first time, begun and completed change. The fishes of the formation present the HOMOCERCAL—that is, the equally-lobed, or one-lobed tail-fin,—a structure peculiar to existing races, with the exception of the shark, sturgeon, and a few others, and form a striking contrast to those in the antecedent groups, which were all possessed of the HETEROCERCAL, or unequally-lobed tail-fin. [Illustration: Heterocercal. Homocercal.] The Permian system of strata has hitherto been noted for the introduction of walking, air-breathing animals; hence it has been a canon of the science, that in these deposits lie entombed the last links of that ancient chain of organic life which prevailed from the beginning, and also the first terms of the new series which attained to such monstrosities and prolific exuberance in the succeeding epoch. Doubtful as to the existence of reptilian and ornithic creatures during the carboniferous period, both forms of creation are here distinctly manifested; and, in the higher members of the triassic group, birds and reptiles have left traces of their path. Thus remarkably defined, in an invariable chronological series, was the new red sandstone formation; all the ancient types of organic life were disappearing; completely new forms had just begun to replace them. But, while we are writing, the discovery has been announced that, so old as the devonian age, reptiles existed; alligator-like foot-prints, in regular alternating order, have been found impressed in the old red sandstone, near Pottsville in Pennsylvania, and by Mr. Lea, their discoverer and American conchologist, the animal which owned them has been named the SAUROPUS PRIMÆVUS. A revolution in geology is decreed in the words. Many divisions in the systems of rocks will have to be revised, many distinctions altogether obliterated, theories of development and of many other things are now sadly misplaced, and out of keeping with the newly-declared order and progress of organic life.[7] But without venturing at present to enter upon the consequences to palæontology involved in this important discovery, we proceed with the known and recognized history of the formation in question.