GEOLOGICAL SUEVEY OF THE TEKRITOKIES. 207 



part of Lincoln Valley. On the eastern slope of this knob appear the 

 overlying beds, consisting of a few hundred feet of thin-bedded ferrugi- 

 nous sandstone, with few fossils, apparently Carboniferous, with a hun- 

 dred feet or more of bright-red sandstones, possibly Triassic, followed 

 by brown and drab thin-bedded limestones, crowded with Fseudomonotis, 

 Lingida, Aviculopecten (#,) &c., which are evidently of Jurassic age. The 

 dip of these latter beds is here 15°, IST. 44° E. ; and no unconformability 

 is e\ddent from the very base of the lower quartzite to the top of 

 the exposed beds. At other points in the neighborhood, however, cer- 

 tain distortions and displacements led me to suspect a partial uncon- 

 formability between the Carboniferous and the Jurassic. 



Passing farther out on the main spur, nearly to the road running from 

 Fort Hall to Eoss's Fork the, older beds mostly disappear, only a thin out- 

 crop of the shelly Jurassic limestones being located by loose blocks in. 

 the soil on the west slopes, while the crest and eastern slopes of the 

 spur consist of white and light-gray Pliocene sandstones and limestones, 

 interlamiuated with trachy tic porphyries and coarse volcanic sandstones, 

 all dipping about north 54P east, at angles varying from 15° to 30°. 

 These dipy, which gave renewed evidence of late disturbance, even later 

 than the commencement of volcanic eruptions in this region, continue 

 with little change to the very extremity of the spur, where the opposite 

 side of the anticlinal fold is also apparent in the basalts, which dip 72°, 

 S. 34° W. The examination was not carried far enough to ascertain cer- 

 tainly whether these tilted basalts are, or are not, continuous with 

 either of the beds which floor the great plain. 



On the east side of Lincoln Valley there is either a small fault or a 

 very sharp double fold. About five miles south of the fort, on the east 

 side of the road to Soda Springs, the Jurassic shaly limestones lie at the 

 foot of the ridge, with a dip of about 35°, N. 19° E., while its higher 

 portions include sandstones and interlamiuated limestones, probably of 

 Carboniferous age, dipping 65°, N. 45° E. A more eastern portion, 

 of this same ridge shows the other side of a synclinal in these same 

 Carboniferous sandstones, dipping 4G°, S. 5S° W. In the axis of the 

 synclinal the Triassic red sandstone shows a thickness of 100 feet or 

 more, at a point about one and a half miles east of Fort Hall, and visible 

 from that post. The most easterly portion of this ridge, approaching 

 the valley of Blackfoot Fork, exhibits another anticlinal and another 

 synclinal, the eastern edge of the latter culminating in the highest point 

 of the outer end of the spur, which received from our topographers the 

 name of Higham's Peak, in honor of the proprietor of the nearest ranch. 

 From this high point it becomes evident that the valley of Blackfoot 

 Fork occupies, for a considerable distance, the axis of a broad anticlinal j. 

 and considerable thicknesses, of Carboniferous limestones are exposed on 

 both sides. The immediate mouth of this valley is rather wide and flat, 

 though the channel of the stream itself is comparatively deep and nar- 

 row, but, from a iioint above five miles up, the stream is for many miles 

 deeply canoned in basalt which floors the valley as a corresponding 

 stream does that of Port Neuf 5 and it is probable that, here as there, 

 the valley has given exit to the overflow of some volcano near its head, 

 which is very near to the head of Port Neuf and the Soda Springs. The 

 extremity of the dividing ridge beyond Higham's Peak consists of the 

 Carboniferous sandstones, nearly or quite to the level of the plain. If any 

 volcanic rocks have ever rested upon it, they have been so thoroughly 

 eroded as to leave no trace ; but the ridge next east of Blackfoot Fork, 

 terminates in a mass of porphyries. 



