HEAD OF SMITH'S FORK. 257 



widening-out of the stream-beds, resulting from the erosion of the softer 

 beds. In the canon of the East Fork, several outcrops of limestone are 

 found, while lower down the stream sandstones, probably Triassic, are seen 

 cropping out from under the gravelly slopes of its banks, overlaid at some 

 little distance still farther north by an earthy limestone, which has been 

 referred to the Jurassic formation. The strike of the Upper Coal-Measure 

 limestones on these spurs is 15° east of south, but must bend northward 

 again to accord with its position on Smith's Fork, though, in the thickly- 

 timbered and gravel-covered plateau between Black's and Smith's Forks, 

 no sufiicient outcrops were found to accurately determine their position. 

 Near the forks of Sawmill Creek, to the north of Gilbert's Meadows, were 

 found some loose fragments of limestone, evidently not far from their 

 parent beds, which resemble lithologically those of the Jnrassic beds. 

 This probable position of the Jurassic beds accords with the idea of a sharp 

 lateral flexure to the north at this point. 



The western side of the valley of Smith's Fork, opposite Gilbert's 

 Meadows, is occupied b}^ an immense lateral moraine, now overgrown by 

 forest, but easily distinguished by its peculiar topograpliy from the gravelly 

 beds of the Wyoming Conglomerate. This, and some terminal moraine- 

 material in the valley, obscure the outcrops of the Upper Coal-Measure 

 limestones; consequently, the first exposures of the underlying rocks are 

 quartzite beds, dipping 42° northward. This dip holds, in ascending the 

 creek, to the point where it foj-ks, beyond which the dip flattens on the 

 west side to 20° for the distance of a couple of miles, and then, at a point 

 marked by a side-ravine, changes suddenly to horizontal, and, farther up, 

 to a dip of 5° to the southward. This side-ravine seems to mark a line of 

 faulting ; but, from the want of any definitely recognizable horizon in the 

 beds of the Weber Quartzite, it is difiicult to determine whether the down- 

 throw has been to the north or to the south. 



The Indian trail, which crosses the range at this point, leading from 

 Fort Bridger to the Uinta Reservation, affords a section which is character- 

 istic of the general Uinta uplift, passing as it does along the western base 

 of its most lofty peaks. Above the steep dips of the northern side of the 

 fold, already mentioned, the head of Smith's Fork is an amphitheatre-like 



17 D G 



