THE EOCENE OF EUROPE AND NORTH AMERICA 129 



It is readily distinguished geologically (Fig. 43) by horizontal alternating 

 bands of gray and bright red fossil-bearing rocks. These red bands contain 

 most of the fossils, and some are of considerable horizontal extent. The 

 basin has been explored successively bj^ Ilayden (1859, 1869), by Wortman 

 for Cope (1880) and the American JXIuseum of Natural History (1891, 1896), 

 by Loomis for Amherst College (1904), and by Granger (1905, 1909) for the 

 American Museum. To the latter we are indebted for the first accurate 

 survey of the geology and of the life succession in this basin as here set 

 forth.^ All previous accounts are incorrect, first, in attributing too great 

 thickness to the Wind River deposits, second, in failure to connect them 

 properly with the miderl3dng Wasatch. 



The sequence of the Wind River life zone to that of the Wasatch is clearly 

 indicated in the Tatman Mountain section (Fig. 38) at the summit of the 

 Big Horn Wasatch deposition (Fig. 41) to the north; here we clearly pass 

 from the Wasatch into Wind River times. 



While these formations were being deposited in Wyoming there was accu- 

 mulating in southeastern Colorado the base of the Huerfano Formation, 

 discovered l^y Hills - in 1888 and explored by Osborn^ and Wortman in 1896. 

 The basin lies immediately north of the famous twin volcanoes known 

 as Spanish Peaks, and the Huerfano deposits are most probably tuffs, or of 

 volcanic dust origin. The fossils apparently occur in a single stratum not 

 exceeding ten or fifteen feet in thickness and not more than thirty or forty 

 feet from the base of the formation. They include the remains of ten genera 

 and of several species characteristic of the Wind River deposits. While 

 the lower Huerfano levels are of Wind River age, the upper levels are dis- 

 tinctively of IMiddle Eocene, or Bridger age. 



The Wind River life has thus been found in three chief localities: 

 Wind River of Wyoming, 500 feet. 



Tatman Mountain, upper levels of 'Big Horn Wasatch' of Wyo- 

 ming, 300 feet. 



Huerfano of southeastern Colorado, 800 feet, including 'Bridger' 

 levels. 



Geographic conditions. — Loomis (1907) has rightly regarded the Wind 

 River Formation as of fluviatile and flood plain origin. The wide horizontal 

 extent of the red bands is attributable to prolonged or repeated periods 

 of flooding; the red color is less probably due to aridity or other atmos- 

 pheric causes than to erosion from the Triassic rocks. Besides a great 

 variety of mammals, the ' red beds' contain turtles (Trionyx), crocodiles 

 (Crocodilus) , and lizards of the family of Anguidse (Glyptosaurus) . The 



1 See also forthfoming Bull. Amer. Mas. Nat. Hist., by Walter Granger. 



2 Hills, R. C, Recently Discovered Tertiary Beds of the Huerfano Basin, Denver, 1888. 



' Osborn, The Huerfano Lake Basin, Southern Colorado, and its Wind River and Bridger 

 Fauna. Bull. Amer. Mus. Nat. Hist., Vol. IX, 1897, pp. 247-258. 

 K 



