120 E E. Clements 



are regarded as indicating a slightly more humid climate with 

 savannah and chaparral such as now occur around the margin of 

 the Great Valley (Merriam, 1916:168). 



In discussing the Virgin Valley fauna, the same author (1911 : 

 206) concludes that the closest relationships are with the Mascall 

 of Oregon and the Pawnee Creek of Colorado, though the simi- 

 larity with the Snake Creek beds of northwestern Nebraska is ac- 

 tually greater. Here again, the ungulates provide the significant 

 evidence, and leave little question that the Great Basin and 

 Middle West were peopled in large part by grazing types living 

 in a climax of mixed prairie, but probably without the short- 

 grasses of today. 



Deformation and Climatic Cycles in the General Region 



A comprehensive account of deformational and cUmatic cycles, 

 with particular relation to changes of climax and the significance 

 of the climax sere or clisere, has been given in Plant Succession 

 (1916: 304, 321, 364). The geological materials for this were 

 drawn chiefly from Chamberlin and Salisbury (1906) and from 

 Schuchert (1910, 1914). In scrutinizing the earlier conclusions 

 in respect to the cHmate of the desert region, further data have 

 been taken from Schuchert (1924), Jones, Antevs, and Hunting- 

 ton (1925), and Antevs (1929). 



For the present purpose, the deformation cycles of direct im- 

 port are three, namely, Paleocene-Lower Oligocene, Upper 

 Oligocene-Miocene, and Pliocene-Pleistocene, forming the long 

 , interval from the disappearance of the Cretaceous Mediterran- 

 \/ ean to the present. The immediate consequence of each cycle 

 was a primary climatic pulsation, in which were involved smaller 

 ones caused in all probability by solar fluctuations. The best 

 known and most pronounced of these were the glacial-inter- 



