246 DISCUSSION OF THE DESICCATION QUESTION. 



investigation in connection with tlie plant remains contained in the most 

 recent formations, including especially the strata usually referred to the 

 "Drift" by geologists, and in which we might expect to find materials which 

 would throw light on the distribution of the different floras of former geo- 

 logical epochs in the region of the Cordilleras. At present it seems to be 

 impossible to draw any general oonclusion, other than that already indicated, 

 namely, that there is proof of a decided lowering of the temperature as we 

 approach more recent times. The genetic connection of one flora with an- 

 other is involved in the utmost obscurity. The intervention of the so-called 

 " Glacial epoch " has evidently nothing to do with it. There can be no doubt 

 that the flora of the Sierra Nevada, for instance, so different from that of the 

 Pliocene epoch, had assumed its present character before the ice took posses- 

 sion of the higher portions of that range. 



The profusion of animal life, during the various epochs of the Cretaceous 

 and Tertiary, in the Cordilleras, has already been alluded to in the preceding 

 pages.* Without attempting to go into details with regard to any precise 

 indications of climatic change offered by the development and disappearance 

 of the successive faunas which occupied that region in later geological times, 

 it will be sufficient to remark that there can be no doubt that, on the whole, 

 the evidence is corroborative of that already presented as furnished by the 

 fossil plants in that portion of the continent. The astonishing profusion of 

 animal life, the large size of many of the species, the predominance of several 

 important genera now limited to the warmer regions of the globe, — as, for 

 instance, the CrocodiUa, so abundant in the Cretaceous and Eocene beds of 

 the West, — all these facts point in the direction of a decidedly warmer cli- 

 mate as prevailing in those earlier days. 



This is emphatically the case in the Sierra Nevada, where the Tertiary 

 strata, as described in the Auriferous Gravels, contain the remains of several 

 genera of land and aquatic animals now limited to regions of considerably 

 higher mean temperature than that of any part of the region at the present 

 time. Among these the rhinoceros and hippopotamus may especially be men- 

 tioned, as also various species of the family of the camel. Nor is the fact that 

 so large a part of Central North America was ranged over by the mastodon 

 and elephant in such great numbers during later Tertiary times to be left 

 out of account in considering the probability of the existence of a higher 

 temperature in the days when those animals abounded. Admitting that the 



* 1. c, pp. 116, 117. 



