Stone — Granitic Breccias of the Cripple Creek Region. 25 



always along the line of dikes. After I learned the secret of 

 the Alhambra rock I was repeatedly able to trace the courses 

 of invisible dikes by "float" consisting of pieces of granitic 

 sand-rock mixed with the other surface wash and debris. 



4. Rhyolite dike situated about two and one-half miles south- 

 west of Cripple Creek, on the top of the ridge lying between 

 Pony and Long Hungry gulches. Elevation about 8800 feet. 



The country rock is a massive granite containing a few inclu- 

 sions of black mica schist. No part of a massive dike appears 

 on the surface, but that this is the outcrop of a rhyolite dike 

 is proved by the following facts, 



The inevitable prospector has located a mining claim on the 

 formation and dug a hole ten feet deep, now half tilled with 

 water. This shows that between walls of granite there is a 

 body of fragmental matter. Most of it consists of granite, 

 but there is also a small admixture of rhyolite. Much of the 

 rhyolite consists of small well worn grains and powder, but 

 here and there are subangular fragments up to two and even 

 three feet in diameter. The rhyolite is somewhat porous. 

 The form of the larger rhyolite fragments is quite irregular, a 

 little inclined to be ovate, but with an uneven surface covered 

 with projecting points and edges barely smoothed at the angles. 

 Many of these rough fragments are scattered over the hillside 

 near : these will be referred to hereafter. 



The portion of the breccia consisting of the older rocks con- 

 sists mostly of granite like that composing the walls of the 

 dike. Some of the larger pieces of granite form cobbles 4 to 

 6 inches in diameter, as round and smooth as any stones on the 

 ocean shore or in the eskers of New England. Much of the 

 breccia consists of a sandstone cemented in its present position 

 into a firm grit. One very smooth pebble four inches in diam- 

 eter was composed of a fine granitic sand rock. The most sur- 

 prising thing is the presence in the mass of numerous pebbles 

 and cobbles of Algonkian quartzite showing the characteristic 

 oolitic appearance of the original sand grains. The rock in the 

 region is largely bare of debris and this makes it easy to find 

 inclusions of the quartzite in the granite if such there were, 

 and none were found. The dike evidently penetrated such an 

 inclusion somewhere in its progress upward. Several of these 

 quartzite cobbles show where, after they had been worn to very 

 round and smooth forms, they had been broken and the new 

 surfaces of fracture had barely begun to be smoothed. 



The distance between the granite walls is only about four 

 feet. Five feet below the surface (down to the water) I found 

 granitic grits indistinguishable from the other grits here 

 described. The dump shows nothing but the same fragmental 

 materials, therefore this breccia reaches down at least ten feet. 

 We cannot admit sedimentary action under such conditions. 



