Bulktin of Labomt&ries of Dmuon Univmity rvoi. 3ti 
of trachyte and trachyte pitehstone, These flows extend 
throughout the valley and to the south are seen underlying 
minor rhyolite masses. From the plagioclase-bearing and quartz- 
less andesite to the acid rhyolite was a long step but this is 
partly bridged by the trachyte interval showing that mountains 
may grow old gradually if not gracefully. But there have been 
other episodes in the history we seek to follow. The crater 
during trachyte time must have been near its present site for a 
great boss of brown trachyte pitchstone still rears it head to 
the southwest of the crater never having been quite concealed 
by the flows of rhyolite. To the south of this peak the rugged 
vertebral column of the range is transversely cut by a dark dyke 
of small dimensions which, though greatly altered may have 
been andesite. Its strike suggests that it may have been de- 
rived from the great boss protruding from the western face. 
This rock compromises matters by leaving out the feldspars en- 
tir»ely and may be called a magma basalt or limburgite. It thus 
appears that the mountain made sundry attempts to restore its 
youth but its hoary summits attest the victory of the acid 
series. 
At the very summit just south of the highest peak is an 
oval crater walled on all sides. Its longer axis is about 400 feet 
long and extends south east, while the shorter diameter of the 
ellipse is 250 feet measuring in both cases across the top. To 
the north east of the highest peak is another depression of a 
crescentic form which probably is also an old crater. 
Now passing west to the opposite side of the valley we en- 
counter the same sequence of limestone and shale strata as that 
on the eastern side of the main range. Near the bottom is a 
shaley stratum which is quite fossiliferous. Some little distance 
above this horizon is another of perhaps twenty-five feet with 
still larger fauna. As we ascend the evidences of life are less 
profuse being chiefly corals of which massive reefs occur at var- 
ious horizons. Toward the top the evidences of metamorphism 
increase till the top becomes compact flint. There is no such 
interpenetration of the superincumbent rock as in the corres- 
ponding situation on the eastern side for the flow is a brown 
