SHEEP MOUNTAIN. 167 



Porphyry penetrate the mass of limestone. On the steep southwestern 

 slope of Sheep Mountain, overlooking Sheep Park, the brecciated surface 

 of the Blue Limestone projects through the White Porphyry. A curious 

 feature of this breccia is the character of its cement, which is crystallized 

 gypsum and quite abundant here, though not noticed elsewhere. The exist- 

 ence of so much breccia at this point would strike the observer on first 

 view as probably due to the action of folding and the friction occasioned 

 by that and the displacement of the fault. Inasmuch as the same phenom- 

 ena are observed, although on a lesser scale, at the contact in Leadville, 

 where the folding action has been comparatively slight, it is probable that 

 it was induced by a fracture of the more brittle portion of the surface of 

 the limestone in contact with the molten intrusive mass at the time of its 

 eruption. The fragments of porphyry in the breccia do not necessarily 

 militate against the supposition, since the shell in immediate contact with 

 the bounding beds might cool and harden and then be broken up by a 

 fresh body of molten porphyry pushing over it. The gypsum cement is 

 an evidence of the passage of sulphurous waters, which would form sul- 

 phate of lime by their contact with the underlying limestone, depositing it 

 again in the crevices of the fragments on the surface. That it still remains 

 here seems to be an evidence that the dissolving action of later waters has 

 not been continued so long as in Leadville, where almost every trace of 

 gypsum hai been carried away. 



On the southeast slope of Sheep Mountain, near the timber-line, are 

 several rounded foot-hills, between which the White Porphyry and the Blue 

 Limestone are exposed in the ravines, while the Weber sandstones form the 

 surfaces of the intervening ridges. A number of prospect tunnels have 

 been run in these sandstones, disclosing irregular shale formations in the 

 beds and a local development of White Porphyry above the regular body. 

 In one of the tunnels the end of this intrusive body is well seen, showing 

 the beds curving around it, as in the intrusive mass of porphyrite on South 

 Mosquito section. The average strike of the beds here is from N. to N. 10 

 W., and the dip from 27 to 30 eastward. 



As this locality presents the most typical development of White Por- 

 phyry outside of the immediate vicinity of Leadville it may be well to 



