260 The American Geologist. April, i897 
blocks is less, a fact accounted for, as above seen, by the up- 
lift of the secondary intrusive. 
The fault planes have an important bearing on the ore con- 
centration in two distinct ways. The larger faults toward 
the west. i. e. nearer the theatre of true volcanic activity, have 
afforded means for introduction (by sublimation) of other 
minerals than those indigenous to the limestone strata. These 
breaks intersect the several ore horizons and may afford op- 
portunity for concentration, and they also afford outcrops or 
surface indications which, in several cases have led to the 
discovery of the real "blankets" of ore below. The second 
w^ay in which the faults contribute to ore accuujulation is by 
interrupting the downward movement of waters carrying- 
mineral in solution. Where the throw has been slight this 
has produced an accumulation in the space between the lower 
and upper intersections of the faulted ore zone with the fault 
plane, thus. fig. 1. These accumulations had been recognized 
by the more intelligent miners, though not explained by them. 
The fault plane, though mineralized, contains less lead and 
more iron (sulphides), and frequently more silver (a fact sug- 
gesting that the silver has had a different origin from the 
lead — perhaps sublimation ). 
The fault planes of this order have also greatly interfered 
with the working of many mines by causing obscurity as to 
the actual nuujber of ore horizons. The apparent number is 
often the result of reduplication, as indicated in fig. 2. Still 
more annoying, and without any compensating advantages, 
are the dip faults, which are even more numerous and far 
less regular than the previously mentioned. A ride along the 
crest of the range from north oi Kelly to the Little Baldy 
Mt., at the north end of the eruptive area proper, reveals a 
very large number of such faults with a throw of from a few 
feet to several hundreds. The reason for these is readily seen 
in the fact that the lateral thrust has not been uniform, but 
greater to the north, so that the edge of the stratified series 
is not parallel with the summit but somewhat diagonal to it, 
crossing from west to east some miles from the northern end 
of the range. What comes to the same thing is the fact that 
the granite uplift was greatest to the north, the metamor- 
phosed material having been squeezed up and occupying the 
