154 Mining Regions of Southern New Mexico. [February | 
caused a certain amount of fritting, a characteristic discoloratiot) 
and the formation of numerous, irregular fissures, cracks ai £ 
seams. Even where the overlying volcanics have been removel | 
by erosive agents, their former position can often be establishel £ 
by the record they have indelibly stamped upon the strata whic f 
were exposed to their altering influence. A large percentage d 1 
the total area is covered with heavy deposits of drift, sometims | 
several hundred feet in thickness, whereby all recognition of wi 
derlying beds is rendered impossible. 
Considering the relations between sedimentary and volcan | 
material as exhibited in this region, it is but natural that the wg 
istence of extensive veins should be expected. In truth, sud i 
veins are found,and by virtue of surrounding rocks they aty 
metalliferous. In the heart of the Black range, at and n®i 
Grafton, well-defined veins traverse the limestones as well as Ù : 
trachytes, bearing definitely characterized gangue and ore. Ls 
quently they lie in contact between the two. Their gangue® 
mainly quartz in this region. As quartz resists decomposili® | 
more successfully than the enclosing walls, the veins can often l 
traced for long distances. Generally they cut the edges of tH 
limestone strata, 7. e., their strike coincides with that of the be 7 
they traverse. Occasional faults and cross veins are produced T i 
the occurrence of dikes, which, in turn, are almost as perst" i 
"in course and continuity as the veins themselves. Near ™ 
working. While these latter carry gold as the paying M° 
ver usually predominates, and gold in excess of a few ounc® 
ton enters only sporadically. At Hillsboro’ the auriferous 
acter of deposits has given rise to the formation of gold-p 
Located within accessible distance from water, they have 
turned to account and are now yielding their precious 
under the persuasive influence of hydraulic mining. o 
On the waters of the Pirches, above Hillsboro’, and at 
valley, the ore deposits show a totally different geogn? 
mineralogical character, although their associations af 
tially the same. While the more northerly mountains hide t 
metallic treasures in well-defined veins which cut throu: : 
across the country rock ; while these veins carry a spec! gs: 
gue with the argentiferous and auriferous minerals dme 
therein ; in short, while they promise to develop into 0” 
