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Red Sandstone of the Diabolo Mountains. 
3 
to the southeast. Beginning at the base, we find the Hazel sandstone 
overlain by the Texan marbles, heavy bedded to flaggy, cherty or siliceous, 
and of various colors. Succeeding these is the dark brown sandstone, 
carrying concretions of iron toward the top, and on this the basaltic rock 
or lava. A quartzite caps these lavas, and is followed by schists and 
shales, and then, unconform ably upon all, comes in the Silurian sand 
and lime. The Potsdam seems to be entirely wanting here, unless it he 
represented by the quartzite and shales, which does not seem to me to be 
the case. It appears to me that the various sections prove that the entire 
portion of this section below the Silurian is also pre-Potsdam, as frag- 
ments of all these rocks enter into the formation of that conglomerate. 
The hills north of the mine show varying conditions. A part of them 
shows the Hazel sandstone at the base, with a thickness of 500 feet, over- 
lain by seventy-five feet of gray conglomerate which is made up of only 
partly rounded pebbles and boulders of Hazel sandstone, and red por- 
phyry, rounded quartzites, angular to partly rounded limestone, brown 
sandstone, quartz, chert, etc., in a brown silico-calcareous matrix. In 
places, however, there are (between the Hazel sandstone and the gray 
conglomerate) remnants of an old red conglomerate, which is sometimes 
as much as eight feet thick. The gray conglomerate is here overlain by 
the Carboniferous limestone. 
A ravine which cuts across these beds follows a fault line, and shows 
on one side the section given above, while on the other appears what I 
take to be the Potsdam grits and sands, capped by a gray sandstone, above 
which are horizontal beds of limestone similar to those opposite. A 
barometric measurement of this limestone showed its thickness to be 400 
feet. At still another locality, this limestone was found resting directly 
on the Hazel sandstone without any other bed being present. The only 
fossils found were Fusulina ; but I think there can be no doubt of its 
Carboniferous age as its petrographic character and horizontally all 
correspond with rocks in the same range which carry an abundance of 
Carboniferous fossils. 
We seem then to have this sandstone, if it really be such, at the very 
base of everything in this section. To occupy the position it does, it must 
either be a sedimentary depo'sit laid down prior to these ancient rocks or 
must be part of an immense boss of igneous material, but of still earlier 
age than the Potsdam. I think its character precludes this latter idea 
and believe that it is, as it appears to be, older than the Texan group. 
I made an effort to trace it still further west in hopes of finding its 
relation to the schists and granites which we have, tentatively, referred 
to the Archsean, but was compelled to give it up before I had completed 
the examination. 
