55 



As regards Paleozoic fresh-water fishes, they may or may not have 

 existed. According to our present knowledge, teliost fishes, al 

 though they have been so abundant in both fresh and marine waters 

 ever since Mesozoic time, had no existence in Paleozoic time. Ma 

 rine ganoids were then abundant, and the Mesozoic, Tertiary, and 

 living fresh-water ganoids may have been derived from some of 

 them by lineal descent through fresh waters, but they probably 

 originated by land-locking from the sea during later periods. 



Viewing the animal and vegetable life of the earth as having been 

 expressed in continuous series of forms, we ought not to expect to 

 find that the geological ages were separated from each other by 

 hard-and-fast lines, as regards the fossil remains of those series 

 which characterize the strata of each age respectively. When such 

 lines appear to be distinct, I think we are justified in assuming that 

 the geological record is incomplete ; or, in other words, that the 

 forms necessary to complete that portion of the series really existed 

 at the close of the one age and the beginning of the next ; but that 

 they are not represented by any discovered fossil remains. 



The division between the Paleozoic and Mesozoic of North 

 America, so far as the geology and paleontology of the continent 

 is yet known, is much more distinctly marked than it is between the 

 Mesozoic and Tertiary. This is especially true as regards plants. 

 The greater part of the peculiar forms which characterized the 

 abundant vegetation of the Carboniferous age seem to have sud 

 denly ceased to exist with the ushering in of the Mesozoic age ; 

 and no representative of the dicotyledonous flora, which was so abun 

 dant in the Mesozoic and Tertiary, and which is so preponderant 

 upon the earth now, has ever been discovered in any of the Paleo 

 zoic strata of the earth. From an evolutional standpoint, however, 

 we cannot suppose that such an extensive and highly organized 

 flora came suddenly into being; and we are left to infer that it was 

 gradually developed somewhere, and during a period prior to that 

 which is represented by the strata which contain the earliest known 

 remains of the kind. The small number of land animals, that are 



