22 Stone — Granitic Breccias of the Cripple Creek Region. 



a breccia composed of the fractured upper portion of a dike,, 

 and below this the dike. Sometimes in the granitic breccias 

 we find kinds of rock which are known to be common as inclu- 

 sions in the granite of the region (e. g. the AJgonkian quartzite), 

 but which do not on the surface appear in the granite near the 

 dike. Some of the dikes in question reveal the dynamics 

 of the process whereby the granitic grits were made. The 

 same materials which in some cases we find as beds covering 

 the steep slopes of the hills, in other cases are found beneath 

 the surface between walls of granite but always capping vol- 

 canic dikes. My inference is that all have the same origin and 

 consist of volcanic ejectamenta that were pushed up slowly and 

 quietly by the dikes. 



Some, perhaps most of the facts here recorded, have been 

 revealed by mining operations since the exploration of the dis- 

 trict by Messrs. Cross, Penrose, and Mathews. 



At first glance one might suppose the granitic breccias are 

 merely a matter of detail. In the sequel they are found to 

 involve questions of stratigraphy, and therefore it becomes 

 necessary to set forth the facts somewhat fully. 



1. The case of a dike that did not reach the surface and did 

 not move after solidification. Elevation 9300 feet. 



Such a dike is revealed in the Arcadia workings on the Lone 

 Star No. 1 claim, situated in Poverty Gulch, city of Cripple 

 Creek. The 125 feet level shows a dike, much decomposed 

 but probably phonolite, which is about three feet wide at the 

 bottom of the drift. The dike rapidly tapers upward so as to 

 end six feet higher in a rather sharp edge, though it sends out 

 some stringers ten feet or more into the schists above, some- 

 what in saw-tooth fashion. The dike-rock solidified fast to the 

 walls and still closely adheres to them, hence has never moved 

 relative to- the walls since solidification. Above the dike the 

 schistose rock is broken by joints running in every direction, 

 but none of these crevices appear to be predominant or the 

 upward prolongation of the fissure occupied by the dike. The 

 appearance, is not as if the earth's crust was bodily broken by 

 a fracture that started from a great depth and extended all the 

 way to the surface instantaneously. The appearance is as if 

 the fracture had been opened progressively by the lava itself 

 as the agent. The lava ended above in a liquid wedge which 

 sent out tongues into every crevice. Then as the liquid rose, 

 according to the law of hydrostatic pressure, it pressed laterally 

 so as progressively to wedge apart the walls, and open the way 

 for the rising lava. Nowhere in the Cripple Creek region has 

 any one discovered proof that the granites, schists, or even the 

 older volcanic rocks, at any depths yet observed, were melted 

 by contact with the liquid lava, though they are usually honey- 



