78 Bulletin of Laboratories of Denison U 7 iiversity [Voi. xi. 
that of the trachyte. It may be suggested that the granite is 
due to metamorphism of preexisting sedimentary rocks fused 
by the action of the immense volcano. In this case, as in all 
others of this portion of the territory, the trachyte flows were 
followed by others of a still more acid nature. It would seem 
that these latter flows were not so much from the crater as 
along a great irregular fissure extending south from the vent. 
A series of waves of such material forming quartz trachyte and 
rhyolite form the abrupt range facing the river and extending 
, four or five miles southward from Socorro mountain proper. 
The foot hills are all of talus conglomerate with boulders of 
various sizes up to i8 inches or two feet in diameter. Appear- 
ances seem to show that at this time the surrounding region 
was under water. Toward the south end of this series a con- 
siderable flow of white obsidian is found and obsidian sheets 
cover poorly cemented detrital material of the same age. The 
most prominent of the hills of the trachyte series lies west of 
the smelter settlement known as Park City and from the west 
affords an abrupt front with basaltiform columns. We have 
called it Pallisade mountain. Plate XI, Fig. i. Pallisade moun- 
tain from the northwest showing recent strata at 3. The fore- 
ground (4) as a granite hill over which the Blue Canon road 
passes. To the southward a spur passes for a mile or more at 
a low elevation toward the Magdalena rail road. This projec- 
tion offers an opportunity for the study of alteration phenomena, 
of which more beyond. In the south-eastern part of the area 
no* evidence of the oldest or andesite period is revealed but in 
the south-western angle at Clemou an aphanitic phase of the 
basic eruptive is left uncovered by the basalt that covers the 
south-west one fourth of the quadrangle and has been eroded 
by the arroyo as well as cut by the railroad. Here too is evi- 
dence of explosive activity in the form of masses of talus con- 
glomerate (See Plate XI, Fig. 2). i. Talus conglomerate. 2. 
basis eruptive. 3. Magdalena Mountains in distance. 
The south-west quarter of the area under consideration, 
as already hinted, is covered with a flow of dark basalt of an 
average thickness of not more than twenty-five feet which, near 
