The Origin of the Desert Climax and Climate iii 



These two floras have but two species in common, or six if 

 those in the related horizon of Yellowstone Park are taken into 

 account. However, this fact is of little significance, chiefly be- 

 cause the Mascall of the John Day and Trout Creek have been 

 critically reworked by Chaney (1925) and MacGintie (1933) on 

 the basis of the newer ecological technique, while the Rocky 

 Mountain floras yet await such scrutiny. Furthermore, whatever 

 element of doubt may reside in species based upon leaf im- 

 pressions, this is largely resolved in respect to genera. Conse- 

 quendy, it is logical to assume that both regions exhibited essen- 

 tially the same deciduous and coniferous climaxes, and that these 

 stretched more or less continuously between the two regions 

 in their respective habitats, while the plateaus and plains were 

 occupied chiefly by grassland and scrub. The continuity of forest 

 was doubtless greater in the Eocene because Fagus, Castanea, 

 and Tilia were present both in the Rocky Mountains and the 

 Pacific Slope, the intervening shrinkage of forest and extension 

 of grassland being promoted by conditions during the Oligocene 

 of the interior. 



Fossil Animals 



The carnivores and insectivores are omitted from the following 

 lists for the various formations, primarily because they bear no 

 direct relation to vegetation as food supply. This is likewise true 

 of the raptores among birds. As dwellers in serai habitats, water 

 birds possess little or no value as climatic or climax indicators for 

 grassland or desert and, in this respect, the value of such ground 

 forms as quail, meadowlark, and turtle dove is none too definite 

 (see Grinnell, 1914, 1923, for the birds of Death Valley and the 

 Lower Colorado) . 



Naturally, the major interest inheres in the ungulates because 

 of the direct response of teeth to type of food and of feet to 



