1883.] Mining Regions of Southern New Mexico. 153 
operation. Reports, vague as yet, fill remote mountains with 
untold wealth, but a short time only may elapse before definite 
knowledge and practical demonstration will separate truth from 
fiction. 
Geologically speaking the structure of Southern New Mexico 
is not complicated when viewed on a large scale, although a thor- 
ough recognition of details would require careful study. Taking 
the general character of the ranges it may be said that they ex- 
hibit a large mass of erupted material which forms their highest 
peaks. Flanking the latter are sedimentary beds, referable mainly 
to the Paleozoic groups. These follow essentially a monoclinal 
arrangement more or less complicated by faults. Sharply defined, 
the ranges trend north and south, end more or less abruptly, and, 
though orographically disconnected, belong to one general period 
of geological disturbance. In elaborating the geognostic details, 
however, a wide field for observation is encountered. Without 
attempting to enter minutely upon a subject which would carry 
us far beyond the limits assigned to this paper, it may be well to 
sketch, in brief outlines, the distinctive features of the region un- 
der discussion. 
Keeping in view the presence of eruptives which form the bulk 
of the mountain ranges, we find the adjacent sedimentary beds 
traversed or covered by the volcanic material in every direction. 
Trachyte, resembling that of the San Juan region in Colorado, 
predominate. Dolerites, in part sanidinitic, are not wanting, but 
subordinate. Dikes of trachyte set across either dip or strike of 
Sedimentary strata, and intrusive wedges of the same material are 
held between the latter. From the main points or lines of issue 
the trachytes have spread in the form of flows, wherever their 
quantity and the surface of the locality permitted. Arranged in 
nearly. horizontal layers, they now cover unconformable sedimen- 
tary beds. Erosion has carried away large portions of erupted 
Material, leaving isolated remnants of flows and again exposing 
the underlying formations. 
pe Among the sedimentary beds those belonging to the Carbon- 
‘fous period are most fully represented, although Silurian 
Parite and the characteristic “ red beds” of Mesozoic age are 
also found. Wherever contact has been established with the 
trachytes, the traces are plainly visible in the limestones predomi- 
"oae ii the Carboniferous series. The influence of heat has 
