Se ee ee ee ae ee ae = 
J. P. Kimball on the Geology of Chihuahua. 383 
rock forms a marked deviation from its common appearance. 
Local dips in the Sierra Rica are variable, though a prevailing 
one to the S.W. seems to be marked within the range of my 
observations, which were limited to a brief stay on account of the 
presence of hostile Apaches. The Sierra Rica lode, in which the 
mine of the same name has been opened to a depth of some 
400 feet, is encased in the fossiliferous series, its highest outcrop 
being on the crest of a prong from which the summit quartzose 
rock of the neighboring mountains has been denuded. The 
lode has yielded rich sulphurets of silver, associated with sul- 
phurets of the base metals, in a quartz veinstone enclosing 
breccia from the walls. i 
On passing out of the Rio Grande — the acclivity of the 
surface again becomes appreciable. e ihuahua road 
crosses the limestone range = the Cuesta de Gato, a depression 
In it some four miles beyond the Mula,* thirty-six miles from 
Presidio del Norte. 
configuration, but without water or visible ae sag 
mountains to the west, including the Cuchillo parado, and the - 
Sierra del Chupadores, rises some-450 feet above it. range 
divide ie another, smaller champaign valley beyond, a reddish 
iluvium is met with, some four miles north of the Gallina 
* Incorrectly laid down on Fleury’s map. 
