3o6 The American Geologist. ^^>'' i^^*- 
ena are very evident near the South Camp district. We may be 
justified in assuming that the range at the northern extremity, 
having been undermined to the west by the vast fluid intrusion 
of basic lava (extending westward many miles) dropped to the 
west, forming, in major outlines, the range as we now see it. 
The andesitic outlyers were radial with reference to the pres- 
ent axis of the range, one being to the east, as well as one to 
the west. In the course of these disturbances there were, very 
naturally, some intrusions of basic lava into the up-tilted area. 
Erosion may have continued this work till the range had as- 
sumed something of its present state, when the second disturb- 
ance occurred. This was acid. It may have been anacharitic 
along a fissure extending somewhat parallel to the edge of the 
andesyte. In any event, it not only spread enormous sheets of 
rhyolyte, acid glasses, obsidian, obsidian tuff in rhyolitic base, 
etc., covering the country at large for many miles and left by 
erosion in some of the nearer buttes, like Magdalena mountain 
and Elephant butte, but it produced a series of hills lying along 
the present western margin of the stratified rocks from Hop 
cafion north-westward. This line of rhyolyte hills is seen west 
of the town of Kelly and at North Camp, north of which it 
forms high conical peaks still nearer the range. This rhyolitic 
uplift evidently played its part in the "warping" referred to, 
and from it dikes intrude themselves into the strata. The edge 
of the overlying strata are greatly disturbed and the faults 
do not obey the same law as nearer the axis ; they even, in some 
cases, come to be dipping to the south, or nearly at right angles 
to the range. These blocks cannot be brought within the em- 
brace of any system of distributive faults. Nor is it a matter 
of warping due to direct uplift, alone, for the subjacent granite 
series at one or both of the eruptive periods mentioned, suf- 
fered great metamorphism and was reduced to a paramorphic 
condition terminating in what appears to be a dioryte, but in 
all cases charged with chlorite, epidote, and calcite. Dikes of 
this secondary intrusive are very abundant and fill an irregular 
series of faults not belonging to the original system. In such 
dikes there are frequently fragments of undigested quartz with 
corrosion phenomena. 
In my earlier paper the effect of the rhyolyte intrusion was 
not sufficiently emphasized. Without anticipating the final 
