PUERCO EPOCH. 



'' Bta.iOi^i. 



Sm.i4 ^74. 



'f: 



thickness, and has an extent of several miles on both sides of the river. 

 From this point the strike is northwards, keep- 

 ing at the distance of a few miles to the east- 

 ward of an escarpment of Wasatch formation. 



It contracts in depth to the northward, and 3 



beyond the Gallinas Mountains I have not ob- •"* 



served it. I 



5' 



It is well developed in Southern Colorado, p 



where Dr. F. M. Endhch* and WiUiam H. Holmes,t I 



of Dr. Hayden's Survey, detected it in 1876. Its §" 



mineral character is there similar to that seen in | 



OS 



New Mexico, and its thickness is much greater. % 



On the Animas River it is 1,000 to 1,200 feet; ^ 



on the San Juan River, near the Great Hog ^ 



Back, 700 feet. The general characters of the 5 



. i 



formation are expressed in the following descrip- » 



tion, extracted from my report to Lieut. G. M. S 



Wheeler.J g 



o 



South of the boundary of tbe Wasatch, the varied g- 



green and gray marls formed the material of the coun- "' 



try, forming bad-land tracts of considerable extent and % 



utter barrenness. They formed conical hills and flat o 



meadows, intersected by deep arroyos, whose i)eri>endic- g- 



ular walls constituted a great impediment to our prog- K 



ress. During- the days of my examination of the region '% 



heavy showers of rain fell, filling the arroyos with rush- § 



ing torrents, and displaying a peculiar character of this > 



marl when wet. It became slippery, resembling soap in g 



consistence, 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 drainage chan- | 



nels are cut to a great depth, and the Puerco Eiver '•^ 



becomes the receptacle of great quantities of slimy look- S? 



ing mud. Its unctuous appearance resembles strongly ? 



soft soap, hence the name Puerco, greasy These soft § 

 marls cover a belt of some miles in width, and continue 

 at the foot of another line of sandstone bluffs, which 

 bound the immediate valley of the Puerco to a point 

 eighteen miles below Nacimiento. 



,s'fnr.52, 



7,I0U'. 



n 



"Anuual Report U. S. Geol. Surv. Terrs., 1875, p. 189. 



t Annual Report of Chief of Engineers, 1875, p. 



t Loc. cit, 247. 



Appendix L L. 



