72 Dr. F. V. Hayden on the Primordial Sandstone 
cal characters. Near the base, the rock is of a reddish flesh 
color, very compact, composed of an aggregation of quartz peb- 
bles, varying in size from a minute grain of quartz to masses 
alf an inch in diameter, cemented with silicious matter. Por- 
tions of the rock contain many pebbles of jasper which appear 
to have been slightly worn before being enclosed in the silicious 
paste. Passing up we find the rock to be arranged in thin fer- 
ruginous layers, slightly calcareous but mostly silicious, with 
many small particles of mica. These thin layers are also charged 
with fossils, as Lingula antiqua, Obolella nana, Theca gregarea 
and Arionellus? Oweni. Many of the slabs were covered with 
fucoidal markings and what appear to be tracks or trails of 
worms. e upper part of this formation as seen in the Big 
Horn mountains, is a rust colored granular sandstone, the small 
silicious grains being held together by a calcareous cement which 
causes the rock to effervesce briskly on the application of an 
acid. In tracing the different fossiliferous rocks, at this locality, 
from the nucleus outward, we can see a good illustration of the 
strict conformability of all the formations from the Potsdam 
sandstone to the summit of the Lignite Tertiary. We see here 
the evidences of ae | two great periods of disturbance, the one 
occurring prior to the deposition of the Primordial sandstones 
which inclined the Azoic rocks, and the other at the close of the 
accumulation of the true Lignite Tertiary deposits when the 
mountain nuclei began their elevation above the surrounding _ 
country. | 
Along the Wind-river mountains which extend far northward 
and form the dividing crest of the great Rocky range, the Pots- 
dam sandstone is quite thinly represented and yielded no organic 
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