jiARviNE.] GEOLOGY VxiLLEY OF THE MUDDY. 183 



total absence of upturned beds, and the undisturbed appearance of the 

 usual Park range fold on the west, would indicate the latter. But the 

 fold spoken of as being found a few miles north of the Butte, as well as 

 the unusual presence of granite masses protruding through undisturbed 

 Cretaceous rocks, would seem to lend probability to the view that the 

 Butte owed its presence to at least a post-Cretaceous disturbance, which 

 folded or faulted the Cretaceous rocks about it, though erosion and 

 deposition since have almost totally obscured the evidence of such action. 

 South of the Butte, however, is evidence indicating the latter origin. 

 Here, between the Butte and the G-rand, is a curious area of Cretaceous 

 beds. It is a true geological basin, the beds dipping toward the center 

 from all directions. The west and south sides are best preserved, the 

 others being confused with lake-beds. This portion is composed of two 

 ridges, their abrupt slopes being presented outward, their gentle slopes 

 inward toward the center, so that, approaching the center radially from the 

 south and west, we would have to rise a hundred feet or more up a steep 

 slope, showing the edges of crumbling shaly sandstones, (some argilla- 

 ceous,) to a harder bed on top sloping gently in the opposite directiou, 

 when another sharp but steep ascent would have to he made before 

 descending again gently to the center and the river ; for the Muddy, 

 breaking through the north edge of the basin, curves around through 

 over half a circle in its very center, finally breaking through the south- 

 eastern side to join the Grand. 



To the west the steep faces overlook a narrow belt of lake-beds, from 

 beneath which appear the Lower Cretaceous beds rising in the Park range. 

 To the south the steep faces overlook the broad alluvium bottom of the 

 Grand, which probably here covets the Lower Cretaceous beds, for just 

 south of the river, near its junction with the Blue, some schist-knobs are 

 indicated by the terraced beds of schist debris. East of the basin, the 

 terraced beds cover nearly everything, but a ravine shows the lower 

 beds dipping 30° westward. Farther east is the area of terraced lake- 

 beds, with a few protruding knobs of granitic rocks. It is across in this 

 direction that section 4 (Plate III) is drawn, extending on to the junc- 

 tion of the two forks of the Troublesome. Beneath the lake-beds here 

 forming the surface, the Cretaceous may dip off north and eastward from 

 the granites, wliich show above the surface here and there, and beneath 

 the lava- covered lignitic beds of the Troublesome. 



Nearly at the steep southern base of the granite butte, and exposed 

 in a small ravine, is a small patch of white saccharoidal or quartzitic saud- 

 stone, lithologically like the characteristic beds of No. 1, £fnd dipping from 

 the granite about 30° southwestward. It not only dips from the granitic, 

 but it lies in a small sharp ravine in the granite, and appears to be 

 folded with the ravine. A little farther out the same beds dip gently 

 toward the granite, its edge facing out over the river, descending to 

 which the beds of the basin are found as before described. (See the 

 small section just above section 4.) A little west of here, aud at 

 the northern end of the basin, a southward dip is also found, which 

 turns west as if curving around the west end of the butte. 



It would appear from these facts, then, that south of the butte, and 

 crossed by the Lower Grand, there occurs a patch of Cretaceous rocks 

 which have been folded into the form of a basin, surrounded on the 

 north, east, and south by the metamorphic rocks, and running up on the 

 Park range on the west, as part of the strata forming that fold, and 

 that the butte itself had been brought to its present position by a fold 

 which has turned up the Cretaceous rocks about its southern slopes; 

 probably about its northern slopes also. 



