J. P. Kimball on the Geology of Chihuahua. 385 
which are of an irregular description, and probably unique. 
These will be described in a future number of this Journal. 
implies. 
In the Dolores pass, by which the road crosses the Santa Eu- 
lalia range, no limestone oceurs, the elevations being entirely of 
caniera of various tints, and distinctly stratified. The cemented 
. tubble, to which allusion has been made, is seen in this pass, 
varying from a coarse to a fine breccia. Such deposits are found 
throughout central Chihuahua under the diluvium of the plains, 
and in low places among the mountains. some places it is 
indurated, and in this condition might easily be mistaken for a 
regular, instead of a recent deposit, and be thought to enter in- 
to the stratification which it never does. 
system are approximately north and south. And the same 
may be said of the whole eastern slope of the Cordilleras all the 
elevations has served to modify the uniform poster of the 
cantera. This uniformity consists in the succession of narrow 
and continuous north and south ridges with foot hills, separat- 
ing broad and, longitudinally, remarkably continuous valleys. 
The whole surface, thus characterized, rises toward the west, 
while the mountains gain somewhat in height and the valleys 
in breadth in the same directi Such is the configuration 
a to the summit of the Cordilleras in this latitude, and it is 
thus almost insensibly reached. The term, Sierra Madre, is for 
this reason seldom: heard in Chihuahua. The western slope in 
pegnhon and structure. Though generally occurring in peeey 
eve i lique 
dip 
- Suc 
of the city of Chihuahua, where the Sacramento river 
