1833. ] Mining Regions of Southern New Mexico. 155 
old-fashioned mines, we here meet with ore bodies of totally dif- 
ferent genesis, different relative position and different minerals. 
Instead of barren gangue and paying ore, we find a deposited 
accumulation of ore varying in value; instead of argentiferous 
veins we have argentiferous deds. 
At Lake valley active work has been going on since the spring 
of 1881. As this district shows more prominent development 
than others of a similar character, it may be well to enter into 
some detail concerning genetic and stratigraphical conditions, 
both of which are of exceptional interest. For the purpose of 
presenting the subject in a more comprehensible manner, a sec- 
tion may serve which has been taken across the strike of the 
ore-body." 
Beginning at the western end of the section we find a portion 
of the trachyte (A), belonging to the range which has broken 
through and partly overflowed heavy beds of quartzite (a). The 
latter are probably of Silurian age. They dip steeply away from 
the mountains until hidden from sight by a series of dark gray 
shales (4). A narrow valley, in which the old camp was located, 
is eroded into the shales, readily yielding, as they do, to disinte- 
grating and transporting agents. So far as could be determined, 
the argentiferous shales of Silver City belong to this horizon. 
Above them light gray and yellow calcareous shales (c) form the 
steep approach to the summit of the first outlying “ hog-back” 
or ridge. The latter is protected by a capping of massive blue, 
silicious limestones (g). This limestone forms the floor, or, using 
mining parlance, “ foot-wall” of the ore-bed (D). Conformable 
in every way to over and underlying beds, this deposit of argen- 
tiferous ore must be regarded as an integral member of the 
series of strata which compose the two parallel ridges or hog- 
backs. Overlying the ore-bed we find a more or less compact, 
whitish limestone, the “ hanging-wall” (e), followed by a succes- 
sion of fossiliferous, argillaceous limestone (fand g), which, in 
_ turn, are hidden by drift (i). About thirty species of fossils were 
here collected, the identification of which refers the series to the 
ower Carbonifercus formation. 
Both limestones which form the walls of the interstratified ore- 
bed, are traversed by ore-bearing veins and seams. Usually these 
1 It must be stated that the section is not made on scale, as no accurate contour. 
i surveys of the surface have been-made thus far—E, 
