GEOLOGICAL SURVEY OF THE TEREITOEIES. 63 



southeast, the inclination of the Lower Tertiary and Cretaceous beds is 

 reversed northwest 15° to 25°, extending to the summits of the monnl- 

 aius, which rise 3,000 feet above the Yellowstone Eiver, and are capped 

 with Carboniferous limestones. 



From the general appearance of the surface of the country, I believe 

 that there was originally much greater uniformity in the inclination of 

 the sedimentary strata, in the aggregate, than there is at present. The 

 volcanic forces which operated at a period subsequent to the elevation 

 of the older sedimentary beds rendered their position much more chaotic 

 in many localities. We have here, within a few miles, the Carboniferous 

 beds, near the channel of the Yellowstone, and the same strata capping 

 a mountain-peak 3,000 feet above it. We have also, in the exposure here 

 and there of a consecutive series of the sedimentary beds, continual 

 proofs of our statement that they originally extended all over the area 

 now occupied by the valley and the mountain ranges that border it. 



The study of the series of sedimentary rocks, so finely Exposed at Cin- 

 nabar Mountain and with such regularity of sequence, reveals another 

 interesting fact — that the Yellowstone Valley may be, in part at least, 

 one of anticlinal origin. We have before shown that the limestone 

 range contracted to a narrow belt near Fort Ellis and Bozeman Pass ; 

 that near the head of Trail Creek the ridge seemed to divide, the 

 north portion of the anticlinal crossing the Yellowstone Eiver at the 

 Lower Caiion, and continuing a little south of east along the sources 

 of the branches of the Yellowstone, as Big Bowlder, Eosebud, Black's 

 Fork. The south portion extended southward along the western side 

 of the dividing range between the drainage of the Yellowstone and the 

 Missouri Elvers. Cinnabar Mountain seems therefore to represent a 

 fragment of the south portion, which has not been concealed by debris 

 or volcanic outflow, or removed by erosion. 



About four miles above Cinnabar Mountain the basalt seems to have 

 poured out over the entire surface, and forms mountain-peaks, rising 

 2,000 to 2,500 feet above the valley. In the sides of some of the foot- 

 hills are exposed from 100 to 300 feet of strata nearly or quite hori- 

 zontal, and apparently modern — not older than Pliocene — sands, sand- 

 stones, and marly clays, overlaid by beds of basalt. They have the 

 davk-brown hue which all the modern rocks seem to have when con- 

 tiguous to igneous outflows. From Cinnabar Mountain, to the mouth 

 of Gardiner's Eiver, about six miles, the Yellowstone Yalley, which 

 expands out on the west side to a width of about two miles, is covered 

 with rounded bowlders of massive granite. The mica is usually black, 

 so that the granites have a somber hue somewhat like ancient trap. The 

 channel of the river is also filled with these huge bowlders, which have 

 probably been brought down from the caiion of the Yellowstone oppo- 

 site Gardiner's Eiver. Just above Cinnabar Mountain, on the east side 

 of the Yellowstone, the more modern beds make their appearance low 

 down on the sides of the mountains, as if the dip of the sedimentary 

 rocks had changed toward the east, and the channel had cut through 

 the intervals of the ridges, exposing the outcropping edges of about 

 800 feet of Tertiary beds of various colors and textures. They are filled 

 with intrusions of basalt. The sides of the hills are covered with the 

 dark debris. Bear Gulch is a deep, narrow canon, which the little stream 

 has cut into the mountain side, exposing the granitic core. Masses of 

 granite have been wrenched from their parent bed and swept down into 

 the valley of the Yellowstone. 

 The third canon is mostly through the granites. They are, as usual, 



