122 ON THE GEOLOGY AND NATURAL HISTORY 
which are composed of cherty magnesian limestone, are very much like those already de- 
scribed in Northeastern Kansas, and contain in great abundance some of the same species 
of fossils, as Myalina perattenuata, and others. I have also seen similar limestones in other 
localities, but no fossils were detected, and though having a Permian appearance, they 
may belong to the upper portion of the Carboniferous. 
The evidence is clear in many localities, that prior to the deposition of the Red Marls 
succeeding the supposed Permian, a very great erosion of the surface of the Carboniferous 
rocks took place. We find, for example, in many localities only a thin representation of 
the Carboniferous rocks, and again a full development, one thousand to fifteen hundred 
feet in thickness. 
Overlying the Carboniferous rocks and equally persistent with them is a series of red 
arenaceous marl beds or gypsum-bearing marls, which are co-extensive with the upheaved 
sedimentary formations 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 Pike’s Peak these beds 
are often removed by erosion or concealed by superficial deposits, but their appearance in 
numerous places shows very clearly that beneath the surface they occupy a considerable 
area throughout the country bordering the mountain ranges, possibly extending entirely 
over the eastern slope. Passing over into the Laramie plains we find that the red marls 
constitute the surface formation of the plain country. It has also been shown from the 
investigations of Messrs. Meek and Engelmann, that these beds are revealed along the 
Wasatch mountains, even south of Lake Utah, furnishing undoubted evidence that they 
belong to the same great deposit. ‘The fact also that one thousand to fifteen hundred feet 
of red arenaceous beds are seen near the sources of Green river, leads to the inference 
that they continue southward far down the Green river valley to that portion which takes 
the name of Colorado, and are in fact a continuation of the extensive red deposits, de- 
scribed by various explorers in New Mexico. 
These red beds are also seen under similar circumstances highly developed along the 
mountains at the sources of the Missouri. There seems to be a change in the lithological 
characters below the Gate of the mountains, the peculiar red deposits disappearing for the 
most part, and a series of irregular layers of silicious limestone with a reddish tinge, and 
with oblique lamine, ripple-mark and other indications of shallow water deposition. It is 
through these layers of rock that the Missouri river cuts its way from the foot of the 
mountains to the mouth of Highwood creek, about ten miles below the falls. They are 
also distinctly revealed around the Judith mountains. Along the Big Horm mountains 
thick layers of gypsum cccur, but the gypsum beds are by no means co-extensive with the 
red deposits, and indeed are present in but few localities. Near the head of Powder river 
