1 882.] 



Central Region of the United States. 



the northward, and it extends to 

 the south-west, beyond the over- 

 lying Wasatch beds. 



It is well developed in Southern 

 Colorado, where Dr. F.« M. End- 

 lich 1 and William H. Holmes, 2 of 

 Dr. Hayden's Survey, detected it 

 in 1876. Its mineral character is 

 there similar to that seen in New 

 Mexico, and its thickness is much 3 

 greater. On the Animas river it c^ 

 is 1000 to 1200 feet; on the San ^ 

 Juan river, near the Great Hog | 

 Back, 700 feet. The general char- § 

 acters of the formation are ex- 2 

 pressed in the following descrip- ? 

 tion, extracted from my report to g" 

 Lieut. G. M. Wheeler. 3 | 



" South of the boundary of the o 

 Wasatch, the varied green and £ J 

 gray marls formed the material of §■ f? 

 the country, forming bad land 3 J 

 tracts of considerable extent and ° | 

 utter barrenness. They formed g, ? 

 conical hills and flat meadows, in- 2 

 tersected by deep arroyos, whose 3 

 perpendicular walls constituted a 

 great impediment to our progress. 

 During the days of my examina- 

 tion of the region, heavy showers 

 of rain fell, filling the arroyos » 

 with rushing torrents, and display- £ 

 mg a peculiar character of this s 

 marl when wet. It became slip- ^ 

 pery, resembling soap in consist- 3 

 ence, so that the hills were 

 climbed with difficulty, and on 

 the levels the horses' feet sank at 

 every step. The material is so 

 easily transported that the drain- 



1 Annual Report U. S. Geol. Surv. Terrs., 



!l 



fjs** 



