MIOCENE TREES 



47 



iii tin- Middle Miocene. So far as the mammals are con- 

 cerned, this is chiefly indicated by the plains fauna. Ow- 

 ing to the generally higher temperature, the air was 

 probably moister than at present, but the moisture may 

 have carried farther, to be precipitated on the mountains. 

 Thus the conditions on the plains and towards the sea 

 may have resembled those of Southern and Lower Cali- 

 fornia to-day, with a comparatively damp atmosphere but 

 little or no preciptation during a considerable part of 

 the year. The desert fauna and flora of the southwest 

 is a highly specialized one. which has certainly not come 

 into existence since the Miocene, at least as regards its 

 fundamental types; so it becomes necessary to postulate 

 a desert region during Miocene times, and no doubt much 

 earlier. Whether we shall ever know much about the 

 Tertiary deserts from fossil remains is perhaps question- 

 able, though we certainly have evidence of a semi-desert 

 fauna, as is illustrated by the large tortoises of the Upper 

 Miocene. The Florissant beds afford us a wonderful 

 insight into the mountain life of the Miocene, and must 

 have a continually increasing significance in relation to 

 the evolution of the fauna and flora of this continent. 

 Most unfortunately, they have as yet yielded no recogniz- 

 able mammalian remains, but T am convinced that these 

 will eventually be found. The beds are far from being 

 exhausted, and comparatively little digging has been 

 done at the place where fragments of a mammal were 

 obtained— a locality which I shall be glad to describe in 

 detail to any one who cares to go and try his luck. In 

 the meanwhile, large collections both of plants and of in- 

 sects, already obtained, remain to be investigated and re- 

 ported upon, but for various reasons the work proceeds 

 slowly. 



