I'EALii.] DESCRIPTIVE GEOLOGY PORTNEUF RANGE. 569 



wliicli themselves are just above tlie dark-green slates that in all prob- 

 ability represent the Cambrian, as named by King, in the region south 

 and v\'est of our district. 



Between layer 23. and the limestones of the pass perhaps the section 

 of Station 77 may be found, unless the quartzites just above are iden- 

 tical with those of Station 77, in which case only the chloritic slates and 

 gray micaceous shales of Station 77 are wanting. This, I think, is the 

 most probable view, as there is probably room for them below this sec- 

 tion. The strike di the beds in the section just given must swerve 

 somewhat to the westward as we follow the range northward, so as to 

 fall beneath those of the summit of Station 76. 



Station 117 was on the ridge next east across Cottonwood Creek. 

 This station was not visited by me, but Mr. Gannett brought in a piece 

 of hard, red micaceous sandstone, which forms the summit of the ridge. 

 Whether this upper valley of Cottonwood Creek is a monoclinal valley 

 or an anticlinal, I am unable to say. It appears to be filled with Ter- 

 tiary limestones and sandstones, which appear to extend high up on 

 the ridge of Station 117. North of the latter station quartzites form 

 the summit of the ridge, showing eastward dips. Above these quartz- 

 ites are laminated limestones, above which are the quartzites of the 

 hills west of Basalt Yalley. These all show eastward dips. I am 

 inclined to think there is an anticlinal and synclinal between the east- 

 ern and western ridges. On the west side of Gentile Valley, on a sta- 

 tion about three or four miles above the head of the caQon of the Bear, 

 a red quartzite, similar to those in Marsh Creek Valley, outcrops, with 

 a western dip. There must, therefore, be a synclinal depression along 

 the eastern "side of the range at this portion of its course, but it has 

 Ijeen so much eroded that it is obscure. Its position indicates that it 

 is a fold east of the one noticed at the entrance of the Portneuf to the 

 caiion from the upper valley. 



Station 131 was located on a hill some eight miles southeast of Sta- 

 tion 133, beyond the end of the range, and I refer to it here only because 

 there are outcrops of limestone on it which show eastern dips. On a 

 ridge running south from the station red quartzites outcrop, dipping- 

 east, or perhaps a little north of east. The rocks on the station are 

 dark-blue limestones, but whether above or below cannot be positively 

 stated. They are probably above, however, and the quartzites are 

 in that case "the same as those in the lower portion of the section of 

 Station 133. The Tertiary (Pliocene?) beds in this region lie between 

 and obscure the older beds lying between the two stations. Quartz- 

 ites also outcrop in the valley of Swan Lake, and are probably the 

 same as those near the station. It will be evident from what has 

 been written that our data in relation to this lower portion of the Port- 

 neuf Eange are somewhat meagre. All we can say is that the western 

 portion is composed of Silurian rocks, while toward the eastward the 

 Carboniferous formation may be present. There are probably several 

 folds which enter into the formation of the mountains. The axes of 

 tliese folds have their directions a few degrees west of north and east 

 of south. The range formed the boundary between the lake that filled 

 Marsh Creek Valley and the lake of Gentile Valley and its northern 

 extension. Basalt and Upper Portneuf Valleys. There was probably a 

 €onnection between these lakes through the Portneuf Canon, and when 

 the lake was at one of its highest levels one arm occupied the synclinal 

 just east of the main northern portion of the range. 



The highest peak in the range is Station 76, with an elevation of 9,115 

 feet. Mount Putnam at the northern end has an elevation of 8,933 feet. 

 The slopes on both sides of the range are steep and rugged. 



