344 EEPOET UNITED STATES GEOLOGICAL SUEVEY. 



"based upon the dark steel-gray basalt which farther on impinges directly 

 against the limestone in the foot of the mountain at Station IX, over- 

 lying or tilling eroded depressions in the breccia-conglomerate. The 

 basalt slopes gradually to the westward towards the Blackfoot, forming 

 the walls of the canon in which the stream is inclosed along this part of 

 its course. The upland basaltic slopes are generally covered with a 

 finely-pulverized brown soil, which nourishes good pasturage. Occa- 

 sionally on some of the higher tables areas of bare, rough-weathered 

 basalt occur, strewn with more or less weathered bowlder-like masses of 

 the same rock. We do not again meet with the breccia-conglomerate 

 nor trachyte after leaving the Three-Pine Creek Canon, the basalt thence 

 continuing southeasterly all along the southwest foot of the range into 

 the upper basin of the Blackfoot. But the recess which penetrates and 

 cuts quite across the range in this vicinity and just northwest of Sta- 

 tion IX, and which marks the site of an anciently -eroded depression 

 across this part of the range, is filled Avith herbage-covered hills, 

 whose peculiar imbricated contour, sloping in the direction of the 

 Blackfoot, recall the characteristic surface-features associated with the 

 breccia-conglomerate, as before noted on Three-Pine and Gravel Creeks. 

 Farther within the recess, and nearly in line with Stations IX and X, 

 a sombre, massive, rounded hill forms a rather prominent landmark in 

 the sag of this part of the range, and which is probably also of volcanic 

 origin. In this connection should be remarked the resemblance of the 

 above-mentioned breccia-conglomerate deposits to certain deposits met 

 Avith west of the Blackfoot, near our southern border, described in a 

 preceding page, and Avhich will probably prove to be identical, and 

 possibly these deposits are the equivalent of the interlaminated Pliocene 

 and porphyritic trachytic beds mentioned by Professor Bradley outlying 

 the Putnam ridge north of Eoss Fork on the border of the Snake plain. 



To the southeast of Three-Pine Creek Canon the range gradually 

 diminishes in height, the soutliAvest face still retaining its abrupt charac- 

 ter, the opposite side of the range falling down OA T er a series of parallel 

 wooded ridges into the volcanic slopes of the basin to the northeast. In 

 the southwest flank of the ridge, at Station IX, a fine exhibition of the 

 Carboniferous deposits is met with, the beds lapping up on the mountain- 

 side and showing a series of dark bluish-gray limestones, Avith irregular 

 nodular masses of black chert and spar seams, and containing Ctenacan- 

 thus, crinoidal columns, Zaphrentis, Lithostrotio?ij &c. The beds in this 

 section exhibit quite variable direction of strike and degree of inclina- 

 tion, scarcely two exposures agreeing, although showing a near approx- 

 imation to a dip ranging from 25° to 40°, S. 40° W. ; the A T ariation in 

 strike ranging from S. 10° E. to S. 50° W., as determined from exposures 

 near the crest and in the outlying ridges to the northeast, Avhile at other 

 points in the Avest slope the beds locally dip at various angles, 45° to 70°, 

 S. 10° W. On the southwest slope, howeA^er, the beds are much inter- 

 sected by cleavage and joint structure, greatly obscuring the true bed- 

 ding, Avhich at few points is satisfactorily reA^ealed. To the northwest 

 of the station an intercalated bed of pale-reddish, fine-grained, laminat- 

 ed sandstone, almost a quartzite, shoAvs in much broken up exposures, 

 Avhich hold a position beneath the limestone occurring in the crest at the 

 station. As before mentioned, the basalt of Blackfoot Valley is seen 

 but a short distance from the foot of the mountain, and it doubtless im- 

 pinges against the limestones at this point. To the northeast similar 

 basaltic Aoavs rise even higher on the flank* of the mountains on that 

 side, concealing the character of the sedimentaries in that quarter. 



From the summit of Station X, Avhich occupies the highest southern 



