282 DESCEIPTIVE GEOLOGY. 



were Fenestella, ZapJircntis, and casts of Orthoceras, too indistinct, however, 

 for specific identification. 



EscALANTE HiLLS AND Yampa Plateau. — Wq now rctum to the flanks 

 of the Uinta Eange proper. The singular depression of Brown's Park, and 

 its continuation to the eastward as far as the Little Snake River, lies, as we 

 have seen, approximately in the axis of the main Uinta fold. The causes 

 Avhicli have produced this depression are at the present day difficult to 

 determine. From the position of the Tertiary beds, it is evident that it 

 existed prior to their deposition, and is the result of forces acting between 

 the close of the Uinta upheaval and the filiing-u]) of these great Tertiary 

 basins. One might suppose an engulfment of this portion of the range, and, 

 indeed, the steep angle of the Tertiary beds on the north edge of Brown's 

 Park proves that some movement of this kind has been going on since their 

 deposition. On the other hand, the shape of the valley of Brown's Park, 

 and its continuation to the eastward, has much of the general outline of a 

 glacial valley, and might be supposed to have been eroded by an immense 

 ante-Tertiary glacier. 



On the extreme Avestern end of tlie escarpment which bounds the val- 

 ley on the south, that is, in the upper part of Brown's Park, the beds of 

 Weber Quartzite have a slight dip to the northward. In this region is found 

 further proof that the course of the river was determined since the Eocene 

 period, in the fact of its leaving the softer beds of the open valley to cut 

 narrow canons in the spurs of hard quartzite on the south, as opposite the 

 mouth of Red Creek and in SwalloAv Canon. In general, as has been seen, 

 the northern face of the hills, which bound the valley on the south, is formed 

 of southerly-dipping beds of Weber Quartzite, whose angle of dip varies 

 from 5° to 10°. 



A remnant of the eastern apex of the main Uinta fold is exposed, where 

 the water-course, draining the eastern side of the divide between Little 

 Snake River and Brown's Park, has cut a gap through the northeastern point 

 of the Escalante Hills. In the little conical hill to the north of this gap 

 are beds -of red sandstone, overlain by drab limestones of the Upper Coal- 

 Measures, dipping 45° northeast, with a strike north 50° west. In the hills 

 to the south, this strike changes abruptly to southwest, and the noi-thern face 

 of East Mountain is composed of beds of coarse red sandstone, while its sum- 



