GEOLOGICAL REPORT. 28 1 



II (more so than to A. Mandanensis). Other fossils are young specimens of Sraphitrs 

 larrifornm, and still others Inocmuuus fratiiMis, both forms of which ;irc in Nebraska 

 confined to No. II. This rock is overlaid by rotten slates and shales, which cannot be 

 distinguished from Nos. 5, 6, and 7 of the foregoing section, and are equally abnormal 

 in their appearance. 



LIGNITE FOKMATIOX. 



On the Upper North Platte, near Sage Creek, and at Bryan's Pass, and extending 

 east to beyond Medicine Bow Creek, I had then observed a heavy formation of sand- 

 stones, including a considerable number of beds of brown coal. In this formation, 

 which reposes upon No. Ill, in a stratum immediately above one of the coal-seams, I 

 found a number of marine shells, some Inoeeramus, of which one specimen appears to 

 be /. ten nil 'meatus, which occurs in No. IV, some Osfrca, of which one at least is a new- 

 species, &c, and from the same series, higher up. I obtained specimens of Ci/fJtnra, 

 and the characteristic Avicitla Xrhnrs/caita. K vans and Shnmard. which occurs in Xos. 

 IV and V of the Nebraska section. 



A Lignite, or, rather, brown-coal formation, also occupies a large portion of the 

 country along Platte River from below Deer Creek to near the Red Buttes, and north 

 and south from there. It is mostly composed of white and light-brownish sandstones 

 and argillaceous shales and slates; in the upper portion, also, of arenaceous shales and 

 shaly sandstones. The most eastern point where I noticed it is where the hill-road 

 west of Fort Laramie enters the valley of Platte River, and in the low blurt's some 

 miles below that point. Here I observed light-colored sandstones, mostly not very 

 compact, interstratined with argillaceous and some arenaceous shales of light and dark 

 gray, bluish, and brown colors, and with seams of carbonaceous shales and brown 

 coal. Even the sandstones contain in places particles of coal. The dip is not uni- 

 form — from 15 degrees upward. 



Up Platte River the formation gains in thickness, and more coal was observed. 

 Heavy strata of mostly wdiite sandstone, alternating with argillaceous shales and slates, 

 and with numerous seams of coal, form prominent escarpments along the river, between 

 Deer Creek and the Platte Bridge. The seams of coal are mostly thin. At one point 

 five of them were observed within a height of less than fifty feet, most of them only 

 from 6 to 10 inches thick; but the shales above and below them were highly carbona- 

 ceous and full of vegetable remains, and some of them might be called impure, slaty 

 coal. At other points the carbon appears to have more accumulated, and the seams 

 become thicker, until they form workable beds of coal. A bed of coal on Deer Creek, 

 near the road, is over 6 feet thick, and has long been known, and occasionally been 

 worked for blacksmithing. A description of the coal will be given below. 



The trend and dip of these strata are variable; mostly off the nearest mountains, 

 and near Platte Bridge, it is toward the east, so that lower strata rise to the surface 

 above that locality. The thickness of the formation cannot be estimated with any 

 degree of accuracy, but must be considerable, and may reach several hundred feet. 



Some sandstones nearer the Red Buttes, No. 3 of the above section, closely re- 

 semble those of this Lignite formation, but may perhaps be older. On the ridge, some 

 miles west of the Red Buttes, the road passes by some prominent exposures of white 



