32 Stone — Granitic Breccias of the Cripple Creek Region. 



lite dikes, the liquid now and then spurted in streams or 

 tongues up into or through the mass of crushed granite, as at 

 dike "No. 4, and there cooled. The upward movement imme- 

 diately began to grind and often to crush these injected bodies^ 



When the upper crust of the lava became sufficiently thick 

 it was broken up and the pieces pushed onward. At first they 

 preserved nearly their original positions relative to each other 

 and they were slickened at the sides and barely blunted at the 

 angles. If this happened near the surface, as at dike No. 2,. 

 the smoothed fragments were pushed above the surface before 

 receiving much attrition and there lay in ridges. But if they 

 were pushed far some of them were crushed and then one by 

 one they were rolled until none of them retained their original 

 positions relative to each other. Those stones that happened 

 to be rolled into many positions received the attrition on all- 

 sides and became round. At the sides of the moving dike we 

 frequently find bodies of breccia composed of mixed granite 

 and lava, and in some cases this is known to reach a depth of 

 several hundred feet. 



The above interpretation leads to many corollaries. It is 

 impossible within the limits of this article to mention more 

 than two. First, erosion has been limited since the close of 

 the volcanic period. In other words, the present outlines of 

 the volcanic ridges and cones of Cripple Creek are substan- 

 tially the same as they were originally. 



Second, a large part of the volcanic action was compara- 

 tively slow and non-explosive. 



Specimens of all the breccias here described, except from 

 Nos. 1 and 12, have been placed by me in the collections of 

 the University of Colorado at Boulder, also of the University 

 of Denver and of Colorado College at Colorado Springs. 

 Investigators will thus find them easily accessible. 



Finally, there is reason to believe that dike ejectamenta of 

 the kind here described are not uncommon. 



Colorado Springs, Sept. 17, 1897. 



