MAEVLNE.] GEOLOGY SOUTHERN END OF WILLIAMS RIVER RANGE. 191 



beds forming ridges running across the main valley, and dipping north- 

 ward, with the valleys of softer beds between partially filled with the 

 terraced beds. Meanwhile, on the west, the flat areas at the base of 

 the high mountain-spurs, and which I have considered as covered with 

 Cretaceous No. 1, have approached the Blue, swinging around to a more 

 eastward trend and northward dip, as if to cross the stream ; while on the 

 east the upper escarpments on the face of Ute Peak are eroded away and 

 come to an end, the lower escarpments rising higher, and exposing more 

 of the face of the main ridge, thus showing the background of the meta- 

 morphic rocks which compose it. When first encountered crossing the 

 valley, the northern Cretaceous ridge dips at an angle of 25° or 30° to 

 the north. A little farther on this is followed by a nearly flat dip, and 

 again by a steepening northward one, showing a reflexed or double 

 curvature of the fold. Besides, on the side toward the Ute Peak ridge 

 the sedimentaries, instead of dipping down toward it, seem to have 

 felt more the action of the fault, and dip slightly away from it, so that 

 the valley is now rather a synclinal than a monoclinal, and a synclinal 

 with the axis dipping northward, and its eastern edge cut sharply off 

 by the great fault which has thrust the archsean rocks so high up upon 

 the east, and brought them in direct contact with the edges of its slightly 

 upturned lower strata. A little further south, and the edges of the 

 Lower Cretaceous quartzites are found swinging across the valley to their 

 broken contact with the wall of rock upon the east, and the road passes 

 over them on to the granites, which then form the whole floor and sides 

 of the valley, though still for a little distance farther some remnants of 

 the sedimentary rocks lying up against the fault on the east side are 

 visible. From here for a number of miles southward the valley still 

 retains its open though profound character. The southern continuation 

 of the Blue Eiver group still rises most ruggedly and impressively 

 on the west, bordered at its base with great morainal masses ; while the 

 lowered spurs of the Ute Peak ridge and adjacent mountains border 

 the valley on the east; the terraced gravels and sands still occupying 

 and concealing the middle portions of the valley. Debris of shales and 

 sandstones was observed at a few points, and may indicate the further 

 presence of some of the Cretaceous rocks. At the junction of Ten-mile 

 Oreek from the west and Snake Eiver from the east — the two principal 

 Iributaries of the Blue — an area of reddish beds occurs; and again, at 

 the very southern sources of the drainage, and forming a portion of the 

 high mountain divide between it and the South Park, a thick series of 

 sedimentary rocks present themselves which are apparently of preCreta- 

 ceous age. Neither sufficient examination was here made either to de- 

 termine their limits ox structural relations, nor to ascertrin whether 

 other similar masses might not be present, the region, which is mostly 

 composed of the archasan rocks, and contains important and interesting- 

 mines, being left for the coming season's investigations. 



It is hoped that in the i^receding pages the main purpose of these 

 reports has been accomplished, viz, to present a description, not only of 

 ■ the surface features of the region examined, but also of its interior 

 structure, as to the nature, position, and extent of the rocky masses 

 that compose it, which will be sufiiciently clear to bo intelligible to 

 the general reader interested in our West. It is further hoped, how- 

 ever, that scattered through its pages may be found some new facts 

 which will ultimately aid in explaining more in detail than heretofore 

 some of the problems of the gradual growth of this portion of the con- 

 tinent, such as the former extent of its lands and waters, and the na- 

 ture of the foldings, dislocations, and erosions which have been mainly 



