BT.jonN.] BLACKFOOT RANGE. 345 



point of tlie range one mile southeast of Station IX, from -which it is 

 sepiirated by an intervening depression, a comprehensive view of tlie 

 range to the northwest is gained, sharply bringing out the volcanic-filled 

 recess between Three-Pine Creek and Station IX, and a wide belt of 

 the range stretching between Station VIII and Blackfoot Peak, more to 

 the north. On leaving the basaltic bench, in the soutlnvest foot of the 

 ridge three-fourths of a mile from the summit occurs a heavy deposit of 

 fragmentary butt" siliceous rock, interbedded with bluish and gray spar- 

 seamed and sometimes brecciated limestone beds, succeeded nearer the 

 crest and in the northeast slope by siliceous limestones, which make up 

 the entire bulk of the ridge. The limestones attbrd characteristic Car- 

 boniferous fossils. The prevalence of minute forms, chiefly Gasteropoda 

 and a few Lamellibranchs, strongly recalling the famial characteristics 

 of the Warsaw beds of the Lower Carbonili^rous in the region of the 

 Ul)per Mississippi. There Avas also found here in some numbers a minute 

 Foramiuiferous form, which is quite unique. The section of these depos- 

 its in Station X ridge reaches a vertical thickness of above 2,000 feet. 

 Although exhibiting local eccentricities which indicate that the beds 

 have undergone a degree of crumpling, the inclination of the strata is 

 quite uniform to the northeastward, or ranging from 15° to 70°, K. 10° 

 to 70° E. Looking toward Station IX ridge from this point, it is evi- 

 dent that the strata in Station X belong to the northeast flank of a fold 

 lying to the southwest of that which runs through the former station, 

 and that the intervening depression occupies the position of a synclinal, 

 which may correspond to the synclinal depression observed along the 

 upper course of Three-Pine Creek, before referred to. 



Passing along the mountain ridge to Station XI, 2^ miles to the south- 

 southeast, the same series of upper limestones continue, showing the 

 same general inclination, or dijiping at an angle of 30° to 45°, X. 15° to 

 75° E. In the crest at Station XI the rock is a rough weathered blue 

 and gray silicious limestone, bearing Producti and JStictopora^ and dip- 

 ping 30°, X. 20° E. This point is about the last high eminence on the 

 range, to the southeast of which the country rapidly api)roaches the 

 condition of a low divide, which projects southward into the basin of the 

 Blackfoot. Descending the southwest flank of the ridge, two lower par- 

 allel ridges are crossed before gaining the basaltic plain, in the flrst of 

 which appears a brown-stained grayish limestone and fine indurated 

 arenaceous shaly layers, containing obscure casts of Lamellibranchs 

 {Aviculopectenf)^ Lingulaj &c., the strata inclining at an angle of 30°, X. 

 45° W. I3ut in the spur just to the westward, corresponding to this 

 ridge, the same ledges are tilted to a nearly vertical position, or di])piug 

 80°, X. 30° E. These ledges are traced some distance along the face of 

 the ridge, the strike cur%'ing in and out, and often forming low combs 

 or hog-back outcrops, the extent of the exi)osure reaching several hun- 

 dred feet, though difficult to determine with accuracy. The outlying 

 and but little lower ridge, which is less than half a mile distant irom 

 the former, is apparently made up of similar deposits, showing brownish- 

 red shaly sandstone and dark, slightly-gritty limestone, Avhich, in the 

 southwestern slope, facing the valley, dips 45°, S. 20° W. Hence, in 

 l)assing from one ridge to the other, the axis of an abrupt anticlinal fold 

 is crossed. Such evidence as is aflbrded by the pooi" condition of the 

 fossils and the lithological pecularities of the beds above described seems 

 to leave little doubt as to their Jurassic age; but to account for their 

 position in relation to the Carboniferous ledges which form the mass of 

 the main nu>untain ridge against wliicli the Jurassic beds iinjnnge, hold- 

 ing ueai'ly the same inclination along the northeast flank of the anti- 



