360 University of California Publications in Geology [Vol. 8 



at that time, or whether the lake waters were collected by streams 

 in the western Nevada region, now a desert country, bordering the 

 Miocene lake. 



There are in the lacustral series occasional strata composed almost 

 entirely of pumice or ash or of a mixture of both, containing little 

 or no other material. Although volcanic agglomerates consisting in 

 part of pumice and ash were doubtless exposed to erosion in neigh- 

 boring areas in lacustral time, it is unlikely that they would yield 

 beds of a purely tuffaceous or pumiceous nature and containing no 

 admixture of erosion products. It is very probable that the strata 

 which consist purely of volcanic products derived their materials from 

 volcanic centers which were active in the general region in lacustral 

 time. 



The lake beds contain an abundance of silicified wood. Silicified 

 trunks of trees several feet in diameter were noted. Trees in consid- 

 erable numbers and of large size appear to have flourished in the 

 region. A number of herbivorous species of mammals are represented 

 in the fossil material collected from the beds. They are such types 

 as horses, camels, deer, mastodons, and rhinoceroses. They indicate 

 a growth, in some parts of the territory at least, of grasses and bushy 

 plants which serve as food for these species. At one locality remains 

 of many species of rodents were obtained. Their presence in the 

 Miocene beds indicates local conditions at least of an abundant growth 

 of ground plants and probably of a fairly moist environment. Plant 

 life in the Cedar Mountain region was therefore in upper Miocene 

 time of greater abundance than it is at the present day, and it is to 

 be presumed from this that the climate was more humid. 



The existence of an extensive water body or water bodies in a 

 region which is now so arid as to contain only small playa lakes, dry 

 most of the year, also suggests a somewhat greater rainfall in the 

 territory in upper Miocene time than at present. Numerous tufa 

 domes embedded in the lacustral beds and having tubular openings 

 of considerable size, indicative of at least local abundance of spring 

 water, are further evidence of greater precipitation. 



That the climate was not one, on the other hand, of very heavy 

 precipitation is indicated by the presence of several species of camels 

 and grazing horses. These forms usually inhabit plains and open 

 country. Their occurrence is evidence that in Esmeralda time the 

 precipitation in parts of the region was probably sufficient to support 

 only a plains vegetation and not a forest cover. While the climate 



