GEOLOGICAL SURVEY OF THE TEERITORIES. 207 



part of Liucolii Valley. Ou the eastern slope of tbis knob appear the 

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

 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 Fseudomo not is, 

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

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

 is evident 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 Koss'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 

 si)ur consist of white and light-gray Pliocene sandstones and limestones, 

 interlaminated with trachytic porphyries and coarse volcanic sandstoues, 

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

 These dip;;, 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 oi)posite 

 side of the anticlinal fold is akso 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 Si)rings, 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 sandstoues and interlaminated limestones, probably of 

 Carboniferous age, dipping G5°, N. 45° E. A more eastern portion 

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

 Carboniferous sandstones, dipping 46°, S. 58° 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; 

 and considerable thicknesses, of Carboniferous limestones are exposed ou 

 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 point above five miles up, the stream is for many miles 

 deeply cafioned in basalt which flooi s the valley as a corresponding- 

 stream does that of Port Neuf ; 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. 



