366 THE GEOLOGICAL HISTORY OF THE 
of some iron-containing mineral, now decomposed and in part 
removed. Soft slate-colored specks and pieces, which are doubt- 
less fragments of the slate formation beneath, are also present. 
The cementing matter of the rock is alight grey powdery 
substance, probably decomposed feldspar, which appears to be 
quite easily removed by the mechanical action of rain. There 
is no effervescence with acids, showing the absence of carbonates. 
Because of its constituent minerals the rock is light grey in 
color, although the joint surfaces are frequently stained a dark 
red by iron oxide. This isa further indication of removal of 
iron oxide; and the absence of carbon from these coarse and 
somewhat porous sandstones when compared with its abundance 
in the accompanying fine-grained argillaceous beds, is suggestive 
of the mutual decomposition of the organic substances and iron- 
containing minerals, and their subsequent removal in solution by 
the underground water. 
The prevalent red color of the overlying Triassic red sand- 
stones, which, without doubt, were derived in large part from 
these older sandstones, is probably due to the subsequent oxida- 
tion and precipitation of these same dissolved iron compounds. 
Because of their relations to adjacent formations, and their 
fossil contents, this series of beds has been regarded as of Lower 
Carboniferous and even of Devonian age.* 
A short distance south of the last outcrop of sandstone, 
greenish-grey compact slates with clean-cut joint planes come 
to the surface in many places along the summit of the ridge, 
and generally underlie the country to the south and west. At 
this locality the cleavage is nearly vertical and the beds 
dip northwesterly at angles of from 20 to 70 degrees. Several 
almost vertical veins of quartz, from one to two feet in thickness, 
lie in the slate along the southern brow of the ridge approxi- 
mately parallel with the cleavage planes of the rock. 
Just below the southern brow, a narrow band of sandstone, 
exactly similar to the coarser beds of Carboniferous sandstone 
above described, crops out at the top of the slope. Its elevation 
“See H. M. Ami, Summary Report of the Geol. Surv. Dept. for 1898. Pp. 180-182. 
