236 F. V. Hayden on the Geology of the Country 
IV. Rep Arrenaceous Deposits. 
Overlying the Carboniferous rocks and equally persistent with 
them is a series of red arenaceous Marl beds or gypsum-bearing 
marls which are coéxtensive with the upheaved sedimentary form- 
ations along the Rocky Mountains. The largest development of 
these beds which I have observed, occurs on the northeastern 
side of the Big Horn mountains and on the west slope of the 
Wind River mountains near the source of the Gros Ventres Fork 
of Snake River. From the Red Buttes on the North Platte to 
gh | 
creek, about ten miles below the falls. They are also distinctly 
revealed around the Judith mountains. Along the Big Hora 
mountains thick layers of gypsum occur, but the 
" ; 
River the aggregate thickness of the gypsum strata is about one 
hundred feet while near the source of Snake River there 15 ® 
thickness from fifty to eighty feet. It also occurs to2 COM 
siderable extent at the foot of the mountains, on La Bonte 
creek, a branch of the North Platte. re 
