144 GEOLOGICAL SUEVEY OF THE TEREIT0EIE8. 



distant, several outcroppings of coal have been found, which would in- 

 dicate the presence of Upper Cretaceous or Lower Tertiary beds. Above 

 the Carboniferous limestones, were several layers of sandstone, clays, and 

 quartzites. The sandstones have been used successfully in the manu- 

 facture of grindstones. There is no doubt that as we ascend the Eocky 

 Mountain divide, beds of comparatively modern age appear. 



The geology of all this region is exceedingly complicated, and must 

 be studied with more care than I could give it, to represent it in colors 

 on a map. This will require a most careful, detailed survey, though the 

 general character of the geology will be found to be as I have presented 

 it in this report. Our journey homeward was so rapid that I could not 

 do more than work out the geological features immediately along the 

 route. The details will be wrought in from year to year, as the great 

 work of exploration goes on. 



As we crossed Black-Tail Deer Creek, in ascending the broad, open 

 valley of the Beaver Head, we could look up the valley to the southeast 

 and see distinctly marked on the horizon, thirty miles distant, the 

 limestone range at the sources of the Black-Tail Deer Creek. The val- 

 ley itself is occupied with a large thickness of the lake deposits, while 

 on the north side the hills are composed of metamorphic rocks, and on 

 the south, far below Wild Cat Canon, we find the Carboniferous lime- 

 stones inclining from the sides of the mountains, the nucleus granitic, 

 with extensive outpourings of trachytic basalt. 



At Eyan's Station the valley closes up for a time, and the passage of 

 the Beaver Head Fork through the trachyte, forms the well-known 

 Beaver Head Carion. The igneous rocks are of great variety and tex- 

 ture. Just below the lower entrance of the caQon, on both sides of the 

 river, there is a beautiful, brittle, light-purplish, and whitish porphyritic 

 trachyte or calico rock. Immense masses of unusually perfect breccia, 

 the angular masses set in a white cement, have fallen down on the 

 sides and at the base of the mountains. As we look up the canon from 

 below, the river seems to rush through a narrow gateway with vertical 

 walls, with dark-purplish basalt weathered into most picturesque forms. 

 Prom one point of view above the canon, the rocks on either side pre- 

 sent the form of animals couchant, which, in the imagination of the 

 Indian, had a resemblance to the beaver ; hence the name which is ap- 

 plied to the river as well as the caiion. Along the canon in several 

 localities are tepid springs flowing down the sides of the oaBon and 

 depositing great quantities of calcareous tufa. About one mile up the 

 caiion, on the west side, there is near the road a, high, nearly vertical 

 exposure of 200 feet of soft, yellow and gray limestones, inclining 10° 

 to 25<^ south of west. In this limestone are layers made up of casts of 

 shells. They are not sufficiently distinct to be identified, but are proba- 

 bly Carboniferous, though the texture of these rocks is different from 

 any I have met with the present season. Eising up from beneath this 

 group of arenaceous limestones are 300 feet of gray sandstones, break- 

 ing off vertically in columnar masses, presenting a singularly picturesque 

 appearance. As far up as the mouth of Horse Plain Creek the reddish 

 and gray sandstones and limestones are seen on both sides of the river, 

 with here and there tremendous outbursts of igneous material. The 

 latter sometimes assumes nearly the usual columnar form of basalt, and 

 forms mountains 1,000 to 1,500 feet high above the river, weathered all 

 over the summits into sharp pinnacles. The igneous rocks rriake fine 

 pictures for the photographer. The river originally flowed along a 

 monoclinal interval, at first separating the sedimentary beds from the 

 metamorphic, but flowing to the northeast, while the trend of the mount- 



