Ee ee ee ey Re Ae ey ea fo 
J. P. Kimball on the Geology of Chihuahua. 379 
table-lands all have a basin configuration, there being toward 
the center a depressed portion usually containing drainage 
water. From the Limpia Mts. to the Rio Grande there isa 
gradual descent—the altitude of Presidio del Norte being 2779 
it.; but, unlike the eastern slope of the divide thus formed by 
the Limpia Mts. or Sierra Diavolo, between the Rio Grande and 
Pecos basins, the declining surface has no conformability with 
the stratification. 
y igneous nor 
axis of elevation.* At least on the Presidio del Norte road, 
the rocks are of a metamorphic aspect where not plainly Cre- 
taceous—their topography being that of erosion. It was upon 
pepe : 
silica produced by voleanic waters, reddish brown porphyry 
and a coarse granitic aggregate of which adularia forms a 
large part.”+ 
However it may be in the case of the Guadaloupe and Sac- 
ramento mountains to the north, the Limpia Mts. near the 31st 
parallel are, as I shall proceed to explain, the last easterly de- 
velopment of what appears to be a metamorphic zone next over- 
lying Cretaceous fossiliferous limestone, and probably included 
ae the Cretaceous series, and known ne —_ * peri : 
and quite overspreading a large portion of the state o a- 
hroa—-that oak, signa fo thoteath of the 28” parallel, and 
as far west as the Grand Sierras. Within this area It is the sur- 
face formation of the eastern slope of the Cordilleras, except 
where local elevations have lifted, « or erosion has bared, lower 
rocks. I traced it west beyond Cusihuiriachic whose e 
determined by Dr. Wislizenus, is only 2181 feet less than that 
of the Cumbres de Jesus Maria—reputed to be the culminating 
point of the north Mexican Cordilleras (8375 ft.){ The peak 
