286 DESCEIPTIVE GEOLOGY. 



and dislocations in the Carboniferous beds than those indicated on the map. 

 Its northern point, lying between Island Park and the western end of the 

 Yampa Valley, whose surface is, as shown on the map, capped bya remnant 

 of the Wyoming Conglomerate, presents abrupt escarpments to the west, 

 north, and east, and would seem to be the flat-topped arch of a fold whose 

 east and western sides have suffered dislocation, the centre of the fold 

 having been faulted up. The western wall toward Green River shows at 

 its base the red quartzites of. the Weber group, and apparently represents 

 the line of a very considerable fault, in which the movement must have 

 been some 4,000 or 5,000 feet at least, smce, on the western side of the 

 river, the red beds of the Triassic seem to approach very near the foot of 

 the escarpment. In Whirlpool Canon, where the Green River runs for a 

 short distance due west in a continuation of the course of the Yampa River, 

 a section of this anticlinal fold is given, in the centre of which, apparently, 

 the rocks of the Weber group are exposed. Plate VIII represents a view 

 of the canon of Lodore, looking up the river, as it would be seen from the 

 northeastern point of the plateau-region, south of Whirlpool Canon, though 

 the original photograph was actually taken from the eastern bank of Green 

 River, just above the junction of the Yampa. The escarpment of the 

 eastern side of the fold represents, as we have already seen, a sharp flexure, 

 accompanied by some faulting similar to that of the southern edge of Section 

 Ridge, in which the limestones of the Upper Coal-Measures, which, on the 

 summit of the plateau occupy an approximately horizontal position, are 

 abruptly broken down on the east, and stand along its eastern base in a 

 nearly vertical position. Portions of this fold to the north, as exposed by 

 the erosion of the Green and Yampa Rivers, are seen in section in Plate 

 IX, which represents a view taken from the eastern banks of Green River, 

 just above its junction with the Yampa, looking westward through Whirlpool 

 Caiion and southward along this escarpment. In the left of the field of 

 view are seen the more massive beds of the Upper Coal-Measure group of 

 the Yampa Valle}^, Avhile in the lower part of Whirlpool Canon are exposed 

 the upper beds of the Weber Quartzite. 



In this somewhat imperfect sketch of the Yampa Plateau, it will have 

 been seen that the system of flat-arched folds, Avith very sharp lateral flex- 

 ures, often resulting in a partial displacement, which prevails in other parts 



