48 



CENUZUIC .AlAMMAL HORIZOA^S 



deposition. Altogether the conditions were unfavorable, perhaps 

 proliibitive, for the deposition of fossils. 



Fauna. — Although not certainly recorded, it appears probable that 

 Wind River B contains Eotitanops horealis, the second kno\\'n stage 

 in the evolution of the Titanotheriidse, the first known stage being 

 Lambdotlieriurn primsevum Loomis of Wind River A. 



4a. HUERFANO FORMATION; LAMBDOTHERITJM AND T TJINTATHERITTM ZONES. 



HOMOTAXIS. 



North America.— 1, Huerfano formation of Hills, 1888 (800-1,000 

 feet, Wortman). 2, Wind River {Lamhdotlierium zone) in part. 3, 

 Lower part of Bridger formation. 



The only middle Eocene deposit east of the Rocky Mountains is 

 that of the Huerfano River basin of southern Colorado (see PL I), 

 first described by Hills ^ in 1888, explored by the writer and Wort- 

 man in 1897, and described by the writer.^ The basin opens into the 

 plains immediately north of the famous Spanish Peaks. The sedi- 

 ments described below as marls, cla^^s, shales, etc., will very probably ^ 

 prove to be of volcanic-dust origin. 



The writer's present conclusion as to the age of this formation is 

 that it began during the Wind River and continued without a break 

 into the period of the lower Bridger formation. 



LOWER PART OF HUERFAXO FORMATIOX ; LAMBDOTHERIUM ZONE. 



(Homotaxis, Wind River.) 



Wortman explored the immediately underlying levels to the east 

 of Gardner, previous explorations having been made to the north and 

 west, and was surprised to fuid a fauna containing none of the forms 

 characteristic of the Bridger level (as chiefly found b}' Hills), but 

 distinguished as of Wind River age by the presence of Coryphodon, 

 Lainhdotherium, Oxysena, Trigonolestes, and other lower Eocene forms. 

 Wortman*^ says: 



These beds of the lower diAdsion are indistinguishable, so far as their general appear- 

 ance and lithological characters are concerned, from those of the upper level. The 

 fossils occur apparently in a single stratum not exceeding 10 or 15 feet in thickness, 

 and not more than 30 or 40 feet from the base of the formation. They underlie the 

 beds of the upper di^-ision with perfect conformity, and there is at present no means 

 of determining exactly where the one ends and the other begins. * * * The exact 

 locality from which the greater number of the fossils of the lower beds were obtained 

 is Garcias Canyon, about 1^ miles south of Talpa or the mouth of Turkey Creek. 



a Hills, R. C, 1888. 



b Osborn, H. F., The Huerfano Lake basin: Bull. Am. Mus. Nat. Hist., vol. 9, 1897, p. 251. 



<• Wortman, J. L., Geological and geographical sketch of the Bighorn Basin. In Osborn, H. F., and 

 Wortman. J. L., Fossil mammals of the Wahsatch and Wind River beds: Bull. Am. Mus. Nat. Hist., 

 vol. 4, 1892, pp. 135-144. 



