30 Stone — Granitic Breccias of the Cripple Creek Region. 



the process, and smoothing the stones. These fragments were 

 not cemented. As the incoherent gravel and cobbles rose 

 above the surface they formed a ridge, which at the base over- 

 lay the adjacent granite, probably in this case to a breadth of 

 less than one-eighth of a mile. But the dike continued to rise. 

 As fast as the upper surface of the lava solidified, it was 

 broken and the fragments were pushed upward in substantially 

 the same way as the granitic fragments had been. The ande- 

 sitic fragments rose through the granitic fragments, pushing 

 them to one side and ultimately forming a ridge which at the 

 sides overlay the granitic gravel and cobbles. Later the ande- 

 sitic matter was cemented into a breccia. In places there is no 

 cement to speak of. 



Similar granitic grits are found at Little Pisgah and other 

 places that might be named, but these will suffice for the 

 present. 



It will be noted that granitic breccias have been found above 

 dikes of rhyolite, phonolite, and andesite only. Outcrops of 

 basalt are well exposed on the American Eagles, top of Bull 

 Hill, also on Galena Hill near Grassy and on Signal Hill, a 

 half mile south of Cripple Creek. In none of these cases did 

 I find any granitic breccias, though the conditions were favor- 

 able for finding them if they ever existed. 



13. Ehyolite dikes at High Park. Elevation about 8,000 

 feet. 



Here are several miles of rhyolite dikes, all capped and bor- 

 dered by grits that consist mostly of granitic fragments, but 

 with the schists and especially the Algonkian quartzite well 

 represented, also they contain some rhyolite. Cross (1. c.) 

 includes these among his High Park Lake beds. They have 

 the same general character as the grits already described. 

 These remarks are intended to apply only to that portion of 

 the lake beds that covers and borders the dikes. At a distance 

 from the dikes the lake beds differ in materials and in various 

 other respects from the parts above and near the dikes. 



Had the grits on Straub and Grouse Mountains and those 

 capping the rhyolite dikes in High Park been examined by the 

 writer without having the other dikes to compare them with, 

 it is not probable that any other interpretation would have 

 occurred to me than that they were of sedimentary origin. I 

 make this personal reference for the express purpose of acquit- 

 ting my friend Mr. Cross from any carelessness of observation. 

 The disputed questions involved are all matters of interpreta- 

 tion. 



We are now prepared to consider more fully the details of 

 the process of making granitic breccias that so closely simulate 

 sedimentary beds. 



