24 LARAMIE BASIN, WYOMING. 
Section of Chugwater and overlying beds in Red Mountain, Wyoming — Continued. 
Chugwater — Continued. Feet. 
Light shale 22 
Heavy, flaggy light to buff sandstone and light shales 30 
Pink massive fine-grained sandstones 24 
Reddish salmon-eolored sandy shales 35 
White flaggy sandstone and red shales 45 
Massive, cross-bedded, fine-grained, monumental salmon sa i tdstone . 1 5 
Flaggy white sandstone and reddish shales 20 
Massive, eross-bedded, fine-grained, monumental, salmon sandstone . 65 
Red shales and red flaggy and massive sandstones 450 
Red gypsum, nearly pure 6 
, Red shale 35 
Gypsum 3 
Red shale 10 
Gypsum 4 
Red shale 55 
Fine banded wavy gypsiferous limestone 5 
Red sandy shale (aragonite crystals) 88 
Gypsum, pure, massive 67 
1,133 
The upper limit of the formation is placed arbitrarily at the base 
of the blue shale below the lowest limestone containing Morrison 
fresh-water fossils. This classification includes in the upper part of 
the Chugwater about 200 feet of an alternation of terra-cotta, blue, 
and buff shales and light-colored sandstones which are not typical 
and are absent in the region farther northeast ; but they appear more 
likely to belong in the Chugwater than in the Morrison formation. 
The gypsiferous member at the base of the Chugwater formation is 
273 feet thick in this section and consists of alternations of gypsum, 
gypsiferous limestone, and red shales, with the massive bed of pure 
gypsum 67 feet thick at the base. In the red clay 20 feet above the 
heavy gypsum bed there are numerous crystals of aragonite in 
hexagonal prisms, usually short prismatic to tabular, and in pene- 
tration twins of the tabular form. According to Knight they are 
pseudomorphs after hanksite. Above the gypsiferous measures are 
450 feet of typical red beds consisting of alternations of red shales 
and red flaggy sandstones. Next above are 378 feet of beds con- 
sisting largely of massive fine-grained salmon-colored sandstones 
with a minor proportion of red shale. These sandstones weather 
with rounded outlines and in their erosion forms resemble the monu- 
mental sandstones of the Casper formation. (See Pis. II, B, and V.) 
In the slopes adjacent to Medicine Bow River 3 miles north of 
Medicine Bow, where the formation has an average dip of 10°, the 
thickness is about 1,300 feet. At the top are about 10\feet of red 
shales, below which are 20 feet of gray slabby sandstone, 100 feet of 
