AET.23 THE ESMERALDA FOEMATION BEERY 3 



The flora is remarkable in containing representatives of six genera 

 of hygrophilous plants, and since aquatic vegetation is largely con- 

 ditioned by the presence or absence of water, it does not conform 

 closely to life zones based upon terrestrial forms. Thus the follow- 

 ing genera found in the Esmeralda formation, namely, Azolla, Typha, 

 Potamogeton^ and C eratophylluTn are all present in the present-day 

 semiarid Upper Sonoran zone; Castalm^ a genus tentatively recog- 

 nized in the Esmeralda flora, occurs in the transition to the Hudso- 

 nian zone; and the sixth genus — Traya — has been extinct in North 

 America since the Pliocene. 



These aquatic plants show conclusively the presence of a permanent 

 water body in western Nevada in the Miocene, and this is reinforced 

 by the presence in these deposits of the leaves of such stream and 

 lakeside types as Salix and Pofulus^ and mesophytic genera such as 

 Cercis. This being so, the plants can not give us much definite in- 

 formation about the regional climate, beyond the fact that it was 

 temperate and there was a sufficient source of supply to maintain per- 

 manent bodies of fresh water. The abundance of silicified wood, the 

 presence of tree trunks said to be 6 to 8 feet in diameter, and the very 

 considerable thickness of coal seams would seem to indicate a much 

 greater humidity than prevails at the present time in this region, 

 and perhaps justifies Turner's picture of the environment of Lake 

 Esmeralda, as he christens it. This is rendered more probable by the 

 wide distribution of diatomaceous beds throughout the Esmeralda 

 formation. Frequently the matrix of the present collection is un- 

 usually rich in fresh-water diatoms. 



Dicotyledonous leaves are prevailingly macerated, coriaceous forms, 

 and are not abundant. Of the oaks, Quescus turneri suggests a chap- 

 parral form; and Gh/rysohalanus, RJvus, and Sapindus are all forms 

 that are at home in a semiarid environment. The sparsity and in 

 general broken character of these last-mentioned forms suggest that 

 they may have been brought into the basin of sedimentation by 

 streams, but the willow and Gerds leaves are equally rare and broken, 

 so that the temptation to press the evidence further than is war- 

 ranted must be resisted, and the conclusion is reached that the pres- 

 ent flora does not furnish conclusive evidence regarding the regional 

 environment. 



AGE OF THE FLORA 



The age of this flora can now be much more decisively indicated. 

 Sixteen of the 22 species of plants recorded from the Esmeralda for- 

 mation are not known in other areas and are therefore of slight value 

 in correlation. The remainder show the following distribution : 



