CBETACE0U8 FACXA. 171 



the first of such remains, the Meniseoessus, has quite recently been 

 discovered. As now generally recognised, the Laramie deposits 

 constitute a series intermediate between the Cretaceous and the 

 Tertiary, the faunal characters, as are principally indicated by the 

 abundant remains of dinosaurian reptiles, pertaining to the former, 

 while the plants point directly to the latter. The angiospermous 

 exogens, whose earliest undoubted remains occur in the Upper 

 Cretaceous deposits, here undergo a very considerable develop- 

 ment, and may, indeed, be said to represent the stock whence the 

 floras of the subsequent Tertiary and existing periods have been 

 derived. "SVe find here many of our most common modem types, 

 such as the oak, beech, poplar, tulip-tree, magnolia, alder, and 

 plane. 



Tertiary Faunas. — ^With the close of the Cretaceous period and 

 the beginning of the Tertiary, we note the most marked of all the 

 organic changes that characterise the different geological epochs. 

 Whole series of animals, from the lowest almost to their highest di- 

 visions, suddenly become extinct, or so nearly verge on extinction 

 as to constitute but a very insignificant element in the succeeding 

 fauna ; on the other hand, groups of equal or greater importance, 

 and which had hitherto no (or but very scanty) predecessors, just as 

 suddenly make their appearance. It would seem as though a fresh 

 start had been taken in the peopling of the earth's surface, so 

 different in many respects are the faunas of the Cretaceous and 

 Tertiary periods. But this difference, as it now presents itself, 

 must not be taken to indicate that it in fact even existed as such. 

 The gaps that now separate the one fauna from the other were un- 

 doubtedly filled by animal types of intermediate grade, of whose 

 existence we shall only be made cognisant when the hiatus which 

 here breaks into the continuity of the geological system will be more 

 completely fiUed in. It is illogical, and directly opposed to the 

 workings of evolutionary force, to conceive of a wide-spread group 

 of animals suddenly appearing and springing into prominence ; 

 and no less illogical to conceive of an equally sudden extermina- 

 tion. Hence, where vast differences Ln the faunas of any two suc- 

 ceeding geological periods present themselves, we have reasonable 

 grounds for concluding that a, long lapse of time has intervened 

 between the close of one period and the commencement of the 

 period (as represented) next succeeding — in other words, that there 



