ENVIRONMENT OF THE TITANOTHEKES 



67 



The excess of iron salts in the red clays may have 

 accumulated and oxidized to hematite during dry 

 climatic cycles; the blue clays were probably deposited 

 in a moister climate, which is less favorable to the 

 concentration and oxidation of the iron. Similar 

 alternations of red and blue clays in the desert basins 

 of Lop and of Sewistan have been described by Hunt- 

 ington, who also associates the colors with the recur- 

 rence of moist and arid climatic cycles. Sinclair and 

 Granger (1914.1) ascribe the color banding of the 

 Wasatch and Wind River clays to a similar cause — the 

 alternation of moist and dry climatic conditions — but 

 they have not found any other evidence of excessive 

 aridity, the fauna of the red and blue bands being 

 the same. The fact that the blue clays of the Wasatch 

 are here and there lignitic and are at some places 

 associated with skeletal remains suggests that they 

 may have been formed during cycles of rather abun- 

 dant rainfall, when the surface of the intermontane 

 basin was prevented from drying out rapidly. That 

 these climatic and physiographic conditions were not 

 local is shown by similar color banding in the Wasatch 



of all the mountain-basin regions. The name "Ver- 

 milion Creek" was applied by King to the Wasatch 

 because of the red color of the rocks through which 

 that creek flows in southern Wyoming and north- 

 western Colorado. 



Microscopic examination of the feldspars in the 

 Wasatch deposits of the Big Horn Basin does not favor 

 the idea of luxuriant subtropical forests and a warm, 

 humid climate, with the formation of a deeply decayed 

 humus, but rather suggests a dry, not necessarily arid 

 climate, with rapid changes of temperature, favorable 

 to splintering of the ledges of hard rock; rapid trans- 

 portation of the fragments for short distances; and 

 burial of these beyond reach of carbonated waters. 



A cursorial ungulate fauna. — This conception of a 

 drier lower Eocene climate in the basins during 

 Wasatch time accords with the successive appearance 

 in this region of four families of the modernized types 

 of perissodactyl mammals — horses, tapirs, lophio- 

 donts, and titanotheres — with light, cursorial limb 

 and foot structure adapted to rapid locomotion and 

 wide seasonal migration. 



Correlation of lower Eocene life zones of Wyoming and New Mexico {after Granger, with modifications) 



New Mexico (Wasatch — 

 "Largo" and "Almagre") 



'Largo" (typical). 

 Eohippus, Menis- 

 cotherium, Am- 

 Vjloctonus. 



'Almagro" (typical). 

 Eohippus, Anaco- 

 don. 



Unconformit3' be- 

 tween Wasatch and 

 Torrejon. In south- 

 ern Colorado "Tif- 

 fany" (typical) . 

 No perissodactyls. 



Torrejon. No peris- 

 sodactyls. Fauna 

 more primitive 

 than in "Clark 

 Fork." 



Evanston (typical Wasatch) 



Green River. 



Knight (typical) . 

 Heptodon, Eohip- 



Wind River Basin (typical 

 Wind River) 



Lambdotherium zone 

 ("Lost Cabin"; 

 typical) . H y- 

 rachyus, Eotita- 

 nops, Lambdothe- 

 rium, Heptodon, 

 Eohippus, Menis- 

 cotherium. 



Heptodon zone ("Lj'- 

 site"; typical) . 

 Heptodon, Eohip- 

 pus. 



Big Horn and Clark Fork Basins 



Lambdotherium zone ("Lost 

 Cabin"). Lambdothe- 

 rium, Heptodon, Eo- 

 hippus, Ambloctonus. 



Heptodon zone ("Lj'site"). 

 Heptodon, Eohippus, 

 Anacodon. 



Systemodon zone ("Gray 

 Bull," typical). Syste- 

 modon, Eohippus. 



Eohippus zone ("Sand Cou- 

 lee," typical). Eohippus 

 (abundant), etc., first ar- 

 tiodactyls, rodents, and 

 primates. 



Phenacodus zone ("Clark 

 Fork"; typical). No 

 perissodactyls, artiodac- 

 tyls, rodents, or primates. 

 Fauna more advanced 

 than in Torrejon. 



End of lower Eocene. 



First titanotheres ap- 

 pear. 



First lophiodonts ap- 

 pear. 



First tapirs appear. 



First horses appear. 



Arrival of modern- 

 ized mammals. 



End of basal Eocene. 



Archaic mammals 

 onlv. 



