FEAix-j DESCRIPTIVE GEOLOGY BANNACK RANGE. 571 



eeous schist. I think there is no doubt that the beds are identical. 

 The dip of the beds in the section just given is approximately east, at 

 an angle of 55°. The strike therefore must be about north and south. 

 This probably curves a little to the eastward toward the south, as we 

 find near the divide to Malade Valley an anticlinal axis which is in all 

 probability the same noted in the canon of the Portneuf. The axis of 

 the range, therefore, lies to the west of the station, and the beds must 

 sink as we go south, for the southern part of the range is made up of 

 the limestones that he above these quartzites. Station 78, just south 

 of 77. is on the micaceous slates that lie below the quartzites and chlo- 

 ritic slates. It is a couple of hundred feet higher than Station 77. 

 South of Station 78 a long ridge connects the northern portion of the 

 range with the southern, on which Station 135 was located. 



Station 135 is on limestones that are probably Silurian. Toward the 

 base quartzites outcrop, probably the top of the Cambrian. The dip on 

 the station is about west. On the slopes leading to the station there 

 appears to be some curving in the strike, so as to make the dip more to 

 the southward or southwest. On the east side of the Malade Divide 

 the dip appears to be from Xorth 17° East to Xorth 27° East. 



Between the two points, therefore, there must be an anticlinal axis which, 

 I think, is the same as that of the northern part of the Bannack Bange. 

 The lowest outcrop noted on the east is a white quartzite, above which are 

 irregular-structured limestones. They soon disappear as Ave get down 

 into Marsh Creek Valley. Bradley considered these limestones as be- 

 longing to the Quebec Group.* I found no fossils in the beds, but they 

 are probably the same as the limestones outcropping south in Malade 

 Valley, back of Malade City. The mountain mass west and south of 

 Station 135 may be partly Carboniferous — the continuation of the Car- 

 boniferous south of Samaria, yet to be described however. The western 

 side of the range and the valley beyond were not examined, and this 

 opinion is, therefore, merely conjecture. 



Xorth of the Portneuf Canon the prolongation of the Bannack Bange 

 is a ridge forming the western portion of the hills west of Mount Put- 

 nam. On these hills the outcrops are obscure ; on Station 80 a gray 

 quartzite shows which is the continuation of one of the quartzites farther 

 south. The dip could not be determined. North of the station the Cam- 

 brian beds seem to disappear beneath Tertiary (Pliocene) deposits, wkich 

 forin the hills south of Boss's Fork of Snake River. They, however, 

 form cappings, for at several places outcrops of limestone Avere seen 

 protruding above the light, white, and reddish Tertiary beds. 



On Station 81, eight or nine miles north of Station 80, basalt is found 

 on the summit of the hills bordering the valley of Boss's Fork and that 

 of Snake Biver. This basalt dips at quite an angle toward the valley 7 

 and on some of the hills appears to be horizontal. The Tertiaries also 

 show dips toward the valley of Snake Biver. South of Station 81 a hill 

 shows outcrops of blue limestone, probably Silurian, with a northern 

 dip. All about the hill Tertiary limestones and sandstones outcrop, con- 

 cealing the older beds. The basalt appears much older than the basalt 

 of Marsh Creek, and its position on the Tertiary (Pliocene?) proA r es it 

 older. It was probably uplifted with the underlying beds, which places 

 its age as subsequent or just at the close of the Pliocene. The source of 

 this basalt is probably some point in the Snake Bi\ T er plain. Basalt is also 

 found in the valley of the Portneuf, extending up the valley from the Snake 

 Biver Valley. This basalt of Station 81 is older. In the former, Professor 



* Report U. S. Geol. Survey, 1872, 1873, p. 203. 



