180 GEOLOGICAL SURVEY OF THE TERRITOEIES. - 



brancli aud near the main stream, ridges of sandstones are exposed by 

 the ravines cutting tlirough the lake-beds. These show a higher dip than 

 the shales to the west, being tipped up eastward at an angle occasion- 

 ally above 30°. The intermediate beds are not exposed, and are quite 

 likely to be shales eroded away more than sandstones. The latter, how- 

 ever, give the character to the horizon, being absent in the shales lying 

 below and to the west. A line of exposures a little east of the main 

 stream shows a dirty, dark, somber-brown sandstone, medium grained, 

 about 10 feet thick. Strike north 20° west, dip 45° northeast. A more 

 continuous line of outcrops (all in the ravines) is about half a mile to the 

 east of the main stream. There are here, beside the line of more prom- 

 inent exposure, several minor ones, all being of sandstones, mostly light, 

 but some dark brown, thin bedded, friable, and though not concretion- 

 ary, strongly resemble the Cretaceous No. 5 in the region near the Hot 

 Sj)rings; the common eastward dip here is from 20° to 30°. Up the east 

 branch, about two miles from the Butte, a small side stream from the 

 north has cut a deep valley, exposing a cliff of a few hundred feet in 

 height upon its east bank, {a in section.) At its base is a uniclinal ridge 

 (strike north 15° west, dip 10O-15o east) which exposes a thickness of 

 about 250 feet of light, gray, friable, thin -bedded sandstones, some perhaps 

 of the consistency of freestones, none thicker than one foot, but mostly 

 shaly. Above, for about 225 feet, and forn^ing the lower portion of the 

 cliff, the beds are shaly, and some almost earthy. A band of about four 

 feet in thickness here is of bituminous shale, quite irregular, and con- 

 tains some thin seams of black but weathered and shrunken lignitic coal. 

 The cliff is capped by about 150 feet of coarse, massive sandstones com- 

 posed of metamorphic dSbris, the characteristic and unmistakable beds 

 of the lignitic group. Though the eastward inclination of the upper beds 

 is small and much less than those below, the transition between the two is 

 gradual, showing a flattening of the fold, there apparently being no uncon- 

 formability anywhere in the series. Here, then, the lignitic must rest di- 

 rectly on the Cretaceous without the intervention of the doleric breccia bed 

 of the Hot Springs. That the latter marks the most natural line of de- 

 markation between the two horizons follows from the entire change of 

 lithological characters which it separates, as well as from the unconforma- 

 bility between them at the Hot Springs, and, so far as known, from the 

 complete change of life which here occurs, moUuscan life giving way 

 to plant life. Near the muddy, however, the line of demarkation be- 

 tween the two horizons is not so well marked. From the fact that in 

 the breccia basin, on both the Grand and Frazier Elvers, a few hundred 

 feet of shaly beds lie beneath the lowest coarse sandstones, and between 

 them and the breccia it becomes no unnatural inference to suppose that 

 the carbonaceous shales which underlie the coarse sandstone escarpment 

 here near the Muddy probably form the base of the lignitic, thus leav- 

 ing the lower sandstones of the ridge below as the probable summit of 

 the Cretaceous. Though no fossils were found in these beds directly, 

 yet sandstones characteristic of No. 5, with fossils, occur just below. 

 No. 5 might thus be taken as probably being very nearly 1,500 or 1,600 

 feet thick, making the total thickness of the Cretaceous here in the 

 Muddy Valley about 4,500 feet. These thicknesses, though checked by 

 scaled distances on the map, may be in error from incorrect estimation 

 of average dips, as so much is 0l3scured by the lake-beds. I think that 

 they maj be much too small rather than too large. 



A little north of the lignitic escarpment, a few exposures indicated a 

 flattening of the formation, as if the lignitic beds might extend north- 

 ward and westward toward the Pass into the North Park, as before in- 



