26 Stone — Granitic Breccias of the Cripple Creek Region. 



5. Rhyolite dike situated half a mile southwest of Phonolite 

 Peak, about two miles north and west from Gillett. Eleva- 

 tion about 10,000 feet. 



At the outcrop of the dike a shaft has been sunk 15 feet 

 into partially consolidated gravel and cobbles with bovvlderets 

 up to 18 inches in diameter, many of the latter being much 

 worn and rounded. Part are of rhyolite, most are of granite, 

 like the country rock. The dike outcrops in a rolling region 

 lying west of the extremities of the ancient glaciers that radi- 

 ated from Pike's Peak. The surrounding country is covered 

 with disintegrated granite. Neither glaciers nor running 

 streams can account for a local deposit of such round stones, 

 and we cannot postulate a lake a few rods in diameter that 

 could have deposited them. 



6. Andesite dike at the reservoir of the Water works, situ- 

 ated on a low spur of Mineral Hill, in the northern part of 

 the city of Cripple Creek. Elevation about 9400 feet. 



The excavation of the reservoir exposed a mass of gravel 

 and rounded bowlderets and bowlders up to three feet in 

 diameter. A few are composed of andesite and schists, most 

 are of granite. The gravel is cemented into a hard grit. The 

 existing excavations do not reveal the full size and shape of 

 the deposit. Apparently it is a body of granitic gravel which 

 forms a cap to the dike and spreads out laterally over the 

 adjacent granite to a breadth of 300 feet or more. If the 

 gravel is composed of dike ejectamenta we must suppose that 

 the stones were pushed above the surface as loose or incoherent 

 gravel. By sliding and lateral rain wash this came to overlie 

 the adjacent granite and then was cemented into a firm rock in 

 its present position. This is proved by the fact that there are 

 no smoothed bowlders of the cemented grit as at dikes Nos. 3 

 and 4. The spaces between the larger 'stones are tilled with 

 crushed granite so compact and firmly cemented that it some- 

 times requires close examination to determine its fragmental 

 character. The size of the deposit is about 300x600 (or 800) 

 feet. 



Mr. Cross (1. c, p. 101) suggests that this gravel was depos- 

 ited in a local lake. For the following reasons I regard it as a 

 breccia or conglomerate composed of ejectamenta pushed 

 upward by the rising dike. 



The stones and bowlders vary much in shape. Some are as 

 round as any beach cobbles, most are only moderately rounded 

 at the angles of fracture, and some preserve almost the original 

 shapes of fracture, being only a little polished and blunted at 

 the angles. Many cobbles are rounder than the stones of small 

 lakes become unless transported by long streams, and we can- 

 not postulate such streams in a small mountain cirque bordered 



