92 REVIEWS 
feet, in the Caballos Mountains, to about 1,100 feet in the vicinity of 
Silver City. ‘To these beds in the forthcoming report the name ‘‘Shandon 
quartzite” is applied. They contain Upper Cambrian fossils. 
Resting with apparent conformity upon the Cambrian is a series of 
limestones goo to 1,200 feet thick. The greater part of these limestones 
contain a fauna allied to that of the Richmond division of the Upper 
Ordovician. In some localities a Silurian fauna appears, but no strati- 
graphic break between these beds and the Ordovician has been recog- 
nized, and the indications are that the Silurian beds do not exceed 100 
feet in thickness. The data at hand are insufficient to warrant the sepa- 
ration of these strata, and the name ‘“‘Mimbres” is given to the whole 
limestone formation. 
Resting upon the Mimbres limestones are shales varying in thickness 
from less than 200 feet in Sierra County to 500 or more in Grant County. 
The abundant fauna of the lower half of the formation is Upper Devonian. 
It is of peculiar interest, as it is the same which was discovered years ago 
in the Ouray limestone in southwestern Colorado by Endlich. It is 
characterized by Camerotoechia endlichi Meek, not heretofore recognized 
outside of the San Juan Mountains. For this shale formation the name 
“Percha”’ has been adopted. 
Lower Carboniferous strata have long been known about Lake Val- 
ley, Sierra County. They have not been found at other localities, notably 
at Hillsboro, Kingston, Cooks, and in the Silver City district. The 
name ‘“‘Lake Valley limestones,” formerly applied to these beds, has 
been adopted by the U. S. Geological Survey. 
The Post-Tertiary stratified deposits of gravels and sands have great 
development in the Rio Grande Valley, where their thickness is some- 
times 1,500 to 2,000 feet. They occupy old valleys, and the materials 
are of local origin. The constituents, which are coarse and angular 
along the borders of the containing depressions, become finer toward the 
axes of the valleys; and where the valleys are wide, as in the case of the 
Rio Grande, the axial portions consist principally of sands and inco- 
herent sandstones. In western Sierra County the coarse gravels are in 
places cemented into a firm conglomerate comparable to that to which 
the name Gila Conglomerate is given in Arizona. Extensive exposures 
of the gravels occur along the Palomas River, and the name ‘‘ Palomas” 
has been adopted for the formation. 
[AuTHORS’ ABSTRACT] 
