Geology of Minivg Cnmi) in Xew Jlexico. — Herrick. 261 
whole north end. The influence of these faults seems to have 
been nil, so far as the ore deposits are concerned. 
Turning now to the more strictly igneous portions of the 
range, it will be remembered that the southern part of tlie 
series is broken by a number of craters. The most northern 
lies near Little Baldy or, more strictly, that peak is a part of 
the limb of a large crater at the head of Hop canon. The ear- 
liest eruptions were of great extent and were basic. The 
crater just referred to is of andesitic tuff, and the great brec- 
ciated masses bear witness to explosive periods of great vio- 
lence and extent. What is true of this crater is apparently 
also true of all the others. Opportunity is afforded for veri- 
fying this belief b}^ a vast series of flows which have been left 
exposed by the cataclysm producing Water canon. This 
profound break on the eastern slope leaves a vast, nearly per- 
pendicular wall facing the west and parallel to the range. 
This wall is composed of a tremendous mass of andesitic brec- 
cia, inclining to the east, bearing evidence of a marvelous out- 
burst wliich must have come from the west in tlie very region 
above described. Above this breccia is a series of flows of 
acid nature, the latest being red rhyolite. 
Further south the same sequence is to be found, though 
much disturbed. The rhyolite was evidently very fluid and 
spread over a very large area, even outside the immediate 
sp'nere of the volcano. The greater part of the western aspect 
of the range is hidden by acid flows which were very wide- 
spread and must have been exceptionally quiet and prolonged. 
These flows were repeated at frequent intervals without in- 
tervening change of level and extended many miles to the 
east. Subsequent erosion has carved outcaiions and left iso- 
lated, butte-like peaks, but everywhere the original continuity 
is visible. Some of these flows were obsidian of nearly a 
white color, others were trach3''tes and interesting trachyte 
pitchstones, while the latest were rhyolitic. A very curious 
occurrence in the vicinity of Texas spring is a breccia of 
black obsidian in a tuff-like magma. Chalcedony in amyg- 
daloidal cavities and veins is very common in this acid series. 
The rhyolite and trachyte series is not mineral bearing, and 
the efforts of prospectors on the vast areas so covered have 
been uniformly futile, though the period of acid eruption is 
