380 J. P. Kimball on the Geology of Chihuahua. 
of Sor ne es — 1,643 feet above the village, and which 
is made up o s formation, thus exhibits its development — 
so high up the aaand Sierras, as to leave a difference of less 
than 439 feet of summit altitude between the point where my 
observations ceased, and the highest point in the Cordilleras of 
this latitude, 100 miles farther west, which a bad state of the 
road rendered it impracticable to reach. Its continuation this 
whole distance indeed, is reported to me as a fact by Mr. John 
Potts of Chihuahua; as well as by Mr. W. S. Keyes of San 
Francisco, who entered the sierras from the Pacific side. The 
te Mr. A. Rémond “em e a series of what he So 
Fee eee 
ees eres 
Cretaceous argillaceous alates represented at <Arivechi “hn 
ich he fe 
the valuable account of his explorations, prepared - Prof. 
itney, bear numerous neering analogies to the so-called 
cantera of the eastern slope.* 
ee 
the country suddenly changes, the arid Cretaceous table land 
east of that point giving way to grassy plains, bounded by 
rugged rocks. The gray Cretaceous limestone here passes out 
of sight, and is covered with a reddish brown, hard, compact 
rock, presenting the anomalous condition of a dense quartz 
pers colored by oo oxyd of iron, apparently not. es 
t ute 
minute irregularly 8 shaped cavities filled with crystalline quartz, 
and coated with brown oxyd of iron which sometimes colors the 
quartz segregations. Thus we have the characters, not of @ 
porphyry, but far may be called a arte age each ri 
due to coop Tarrginous ca c oe this 1 ich goes i to machen 
its peculiar topography throughout its wide naa ee No- 
eis to greater advantage can it be witnessed than In 
pass, where the faces of the bluffs are weathered into massive : 
columns, reaching in many cases from their base to top, # 
* Notice of Geological Explorations Northern Mexico made during the year 
1863-65. Pre Ot hed Be si Sex: 
