64 GEOLOGICAL . SUEVEY OF THE TEERITOEIES. 



of a great variety of textures, but largely massive feldspar. Between 

 the Yellowstone and Gardiner's Eiver, commencing at the junction, a 

 wedge of land commences, which rises to the height of 2,000 feet or 

 more with great regularity. This is a portion of the belt of modern 

 sedimentary beds, as shown on the east side of the river, below the 

 junction, as exposing an outcropping thickness of about 800 feet. The 

 Yellowstone makes a bend to the eastward at this point, running out- 

 side of the belt of sedimentary strata, and carving its channel out of 

 granitic and volcanic rocks. The latter are composed of basalt, basaltic 

 conglomerate, and the deposit of Hot Springs. Gardiner's Eiver, al- 

 though diverging but little from a parallel, seems to flow through a 

 monoclinal interval, exposing a clean, wall-like front of 1,200 feet, on the 

 east side, of Cretaceous and Tertiary strata. The dip is slight, 10°, but 

 toward the northeast, and as we ascend the river, lower beds are exposed, 

 until at least 1,800 feet of Cretaceous and Lower Tertiary beds are brought 

 to the surface .within a distance of six or eight miles. Local intercalated 

 beds of basalt are also exposed toward the summit of the hill, and near 

 the forks of the river a heavy bed of the basalt, quite compact, rests hor- 

 izontally on the inclined edges of the strata. There were found here 

 quantities of obscure fossils, among them, a species of Ostrea^ and a num- 

 ber of impressions of deciduous leaves, all of Cretaceous affinities. At 

 another locality a layer of shells was found, and among them Mr. Meek 

 detected Corhula pyriformis, a species occurring near Bear Eiver City, 

 which is regarded as of estsary origin, and of Tertiary age. At another 

 point I found upon the side of the hill, on the east fork of Gardiner's 

 Eiver, Amonites, Baculites, and Inoceramus. There is little or no lime 

 in this great group of beds, simply alternate beds of sandstone, arena- 

 ceous clays, passing down into the dark somber clays of the Cretaceous. 

 As we descend in the series, the rocky layers diminish, and the indurated 

 clays increase, until near the' forks of Gardiner's Eiver, the darl?: Creta- 

 ceous clays are 500 feet thick. The sides of the bluff hill are deeply fur- 

 rowed. This inner ridge, which we have just attempted to describe, is 

 one of the finest exx^osures, as a vertical section of strata, that I have met 

 with in this portion of the West. These beds are only a remnant of a 

 former period, isolated monuments covering a very restricted area; 

 whereas they must have extended across the river, and all over the 

 portion now occupied by the mountains to the westward of the sources 

 of the Missouri. The lower beds of the Cretaceous with the Juras- 

 sic and the Carboniferous inclusive, incline from the east side of the 

 mountains, and dip under Gardiner's Eiver; It is through the latter 

 beds that the waters of the White Mountain Hot Springs come to the 

 surface. Just above the junction of Gardiner's Eiver with the Yellow- 

 stone, on the east side, a seam of earthy lignite six inches thick crops 

 out. Below it is a layer of oyster-shells, and above it are impressions of 

 deciduous leaves. The local detritus all over this valley is so extensive 

 that it deserves continual notice. It seems to fill up the irregularities 

 of the surface, especially in the vicinity of the streams. The section 

 made by the river reveals 50 to 100 feet at times, filling up old ravines 

 or gulches worn out of the basis rocks. 



Before proceeding further with the general geological features of this 

 country, I will attempt to describe, with as much detail as possible, one 

 of the most remarkable of the many marvels of this wonderful valley. 



I have just described, with some minuteness, the high wall of Cre- 

 taceous and Tertiary beds on the east side of Gardiner's Eiver, which, 

 in itself, is well worthy of careful attention. Upon the opposite side of 

 the river, on the slope of the mountain, is one of the most remarkable 



