402 REPORT UNITED STATES GEOLOGICAL SURVEY. 



clinal B, with which they are apparently conformable. The same series 

 of deposits, indeed, recur in the northeast border slopes of the Fall 

 Creek mountain-basin, where, however, they appear in an inverted posi- 

 tion, and merge into the plant-bearing gray sandstones of the Laramie (?) 

 Group. The southwestern flank of this flat-topped uplift is not well 

 seen, but it appears to decline gradually into a narrow belt of greater 

 disturbance, where its component strata again begin to rise. Perhaps 

 half a mile below the upper basin these strata are suddenly uplifted 

 and toppled over past the vertical on the northeast side, sweeping over 

 in an undulating, gently-inclined arch, and pitching steeply on the 

 southwest flank, the fold, as seen in the north side of the valley, pre- 

 senting the appearance indicated in the diagram at E. The exposed 

 strata in the above uplift are apparently identical, lithologically, with 

 the upper horizons in the broad-topped fold D. One or both of these 

 folds reappear in the broad ridge between Station XXYII ridge and 

 Mount Caribou, the comparatively gentle summit slopes of which may 

 have been determined by the moderately-arched strata which form the 

 roofs of these arches. The latter feature was distinctly displayed from 

 both of the above-mentioned points of observation, which, but for the 

 forests, commanded unobstructed view over this elevated mountain tract. 



Once within the upper basin of McCoy Creek the lithological charac- 

 teristics change, a heavy series of, however, comformable deposits, con- 

 sisting of gray, shaly, spar-seamed sandstones and variegated shales, 

 thrown into sharp folds (F and G), succeeding and approaching Mount 

 Bainbridge, preserving uniform southwesterly inclination, as has already 

 been noticed. 



Overlooking the low hills along the north side of the main western 

 branch of McCoy Creek, and which extend over the low water-shed into 

 John Gray's Lake basin, a fair exhibition of the sedimentary rocks there 

 occurring is presented from the summit of Mount Caribou. This re- 

 gion embraces a radius of about one-eighth of a circle, and continues 

 the section from about the southwest dipping horizons between that 

 mountain and the anticlinal (G) next east. The section, as seen from 

 this distance, is conspicuous for the predominance of red-colored strata ; 

 but its chief interest is derived from the rather complicated structural 

 features which the exposures reveal, and which are worthy of attention. 

 Descending into John Gray's Lake basin from the low ridge southeast of 

 Station XXVIII, the, dip of the strata was uniformly to the southwest- 

 ward, gradually flattening out as we progressed in that direction ; but 

 in the above-mentioned quarter it is apparent a far less simple state of 

 things exists. Outlying, or rather continuing the southwesterly inclina- 

 tion of the gray sandstones and wider belts of pale red softer deposits 

 which recline on the southwest flank of the anticlinal fold G, the strata 

 are observed gradually steepening the angle of their inclination, until, 

 at a point about northwest of Station XXVIII, a belt of these red beds 

 shows the strata tilted into positions wavering to one or other side past 

 the vertical, followed by a broad belt of similar colored strata dipping 

 to the norteastward. This has the appearance of a pinched synclinal, 

 but a closer examination might resolve it into a more regular trough- 

 like fold. Immediately to the southwest a heavy deposit, consisting of 

 red and light-drab strata, rises up into the crest of the watershed, where 

 they form a rather sharp arch, succeeded by a heavy series of red beds, 

 which latter dip more and more moderately as they near the borders of 

 John Gray's Lake plain, precisely as has already been seen in the slopes 

 south of Station XXVIII. In both the lithology and magnitude of the 

 folds there is a, striking and most intimate resemblance to the section 



