MARVLN-E.] GEOLOGY NORTHERN LIGNITIC AREA 171 



four miles below the Spriugs. These extend in broad terraced surfaces 

 far up the Williams Eiver Valley, forming all the flat lower and treeless 

 portion of the yalley. The southern and eastern borders of the valley 

 appear to be wholly of metamorphic rocks, which rise in massive spurs 

 and slopes to the Mount Byers ridge ; and though the upper caiions of 

 this drainage cut deeply into these rocks, a uniformity of contour is 

 pretty well preserved among the great spurs. Though not examined 

 directly, some appearances on the eastern border of this valley seem to 

 indicate the presence of the lower Cretaceous beds resting on the arch- 

 ffian rocks. The western side of the valley is of the lignitic beds which 

 com;iose the Williams Eiver Mountains, and which dip gently north- 

 eastward and probably beneath the lake-beds of mid-valley. At the 

 south a great north and south fault occurs, in which the west side has 

 dropped several thousand feet, leaving the metamorphics on the east 

 and the lignitic on the west. The fault probably dies out in coming 

 north. It will be referred to more in detail when speaking of the geol* 

 ogy of the Blue River Valley. The details of the Williams Eiver Valley 

 were not studied. 



THE NOETHEIIN LIGNITIC AREA. 



The lignitic beds v/hich have been described as occupying the '• brec- 

 cia basin " above the Hot Springs, and as lying unconformably upon 

 its western arm as well as upon the Cretaceous below in the nearly hori- 

 zontal beds of Mount Bross, spread out in their northern extension, and 

 form the greatest continuous area occupied by any one geological forma- 

 tion expressed upon the map, except that covered by the arch£ean rocks. 

 Throughout this area, except along its eastern edge, the rocks are but 

 very slightly disturbed, their inclination being generally less than ten 

 degrees and being in various directions, though mostly northward. 



Though the region as a whole is one of elevation, its surface is uneven 

 and rises in four principal masses, which stand high above the interme- 

 diate country. This unevenness is due wholly to the, erosion having 

 eaten farther down into the mass of nearly horizontal beds in certain 

 areas than in others, and this erosion has been thus directed along these 

 channels by the intrusion of eruptive rocks rather than by more pro- 

 found structural causes, as folding, &c. The southernmost and lowest 

 of these four elevated points is the White Face and Coral Peak mass, 

 lying a few miles north of the Hot Springs, which has withstood erosion 

 better than the surrounding country, and hence retained its elevation 

 in virtue of the protective cap of hard basaltic lava which here covers 

 the softer lignitic sandstones. The divide between the middle and north 

 parks is also naturallj^ elevated, but it attains special height at two 

 points : one, Park View Peak, which, though higher than any of the 

 others, is composed of a smaller mass, and hence has more abrupt slopes ; 

 and another, the great mesa-like mountain mass lying west of the Park 

 View, and between the head- waters of the Troublesome and the Muddy. 

 This latter elevation is due to a great capping flood of basaltic lavas 

 covering the lignitic, while Park View and the divide adjacent, though 

 having no lava-cap, is intersected by great dikes of jjorphyritic tra- 

 chyte, which give to it its sharpness as compared with the other and 

 lava-capped masses. The fourth elevated mass of lignitic strata is the 

 high and exceedingly even-topped ridge which is almost completely sur- 

 rounded by Willow Creek and its principal eastern branches. Though 

 unvisited, this ridge appeared to be caused less by the presence of erup- 

 tive rock than by the fact that the drainage, and hence the erosion, had 



