STRATIGRAPHY. 25 
red sandy shales, 8 feet of gray slabby sandstone, 30 feet red shale, 
2 feet of gray slabby and ripple-marked sandstone, 3 feet of red 
shales, 8 feet of soft gray sandstone, and a thick succession of red 
sandy shales and soft red sandstones. Toward the base are several 
thin-bedded sandstone members 5 feet or less in thickness. 
Gypsiferous member. — On Sand Creek the gypsum measures are 
not prominent, but ledges of this mineral from 2 to 4 feet thick, 
associated with and locally replaced by gypsiferous limestone, crop 
out on the red point north of the North Park road crossing and at 
localities east and south of that place. At the bottom of these 
exposures there is a wavy gypsiferous limestone winch is supposed 
to represent the Forelle. This assumption is strengthened by the 
occurrence of aragonite crystals on the hill slopes above the lime- 
stone in a position similar to that which they occupy in the Red 
Mountain section. A mile southeast of Sportsman Lake there is an 
outcrop of gypsum, apparently lying above wavy gypsiferous lime- 
stone that can be traced northward with certainty into the Forelle 
limestone, which crosses the railroad at Forelle. At a point north- 
west of Forelle and west of the line of outcrop of the Forelle limestone 
a well 333 feet deep is reported in the red beds and gypsum measures 
that doubtless lie above that limestone. 
In the Centennial Valley the gypsum measures are represented by 
a thin gypsiferous limestone bed, separated from supposed Forelle 
limestone by red shales. They are overlain by alternations of red 
shale and soft red sandstones. The upper part of the formation 
includes the monumental sandstones as in other portions of the 
region. 
Upper limestone. — In the northern part of the Laramie Basin 
region there is a thin but conspicuous bed of limestone in the upper 
part of the Chugw r ater formation. It thickens to the west and is 
conspicuous in the Freezeout uplift, where it lies a few feet below r 
the Sundance formation. 
Age. — The age of the Chugwater formation is not definitely known, 
but has been supposed to be in part at least Triassic. In other 
portions of Wyoming it includes in its lower portion a limestone 
known to be Permian in age, and in the Bighorn region limestone 
150 feet below the top of the formation contains supposed Permian 
fossils. The fact that the formation is underlain by similar red 
beds of the Casper formation in the southern portion of the Laramie 
Basin throws no light on its age, for in this area red beds may have 
continued to be deposited from Pennsylvanian through Permian 
and into or through Triassic time. 
a In the sense in which that term has been used m the Mississippi Valley. 
