104 GEOLOGY AND MINING INDUSTBY OF LEADVILLE. 



Trias, dipping 15 to 20 east and north. Two other beds of limestone at 

 least are found in this formation, on the same line of strike southward along 

 the western face of Silverheels and in the valley of Beaver Creek, and they 

 may occur here in some of the numerous covered gaps in the section. 



Silverheels Massive. In order to complete the somewhat meager data 

 obtained upon the upper member of the Carboniferous group on this 

 side of the range, the observations made in the region west of the Platte 

 Valley will be next recorded, comprising in this the eastern portion of 

 Mount Silverheels and Beaver Ridge, with the included valley of Beaver 

 Creek. 



In a general way the eastern half of Mount Silverheels may be said 

 to be Mesozoic, in great part probably Triassic, while its western face be- 

 longs to the Upper Coal Measures, and Beaver ridge to the Weber Grits. 

 The included porphyry sheets in the former rocks have a more recent and 

 trachytic appearance, like that found at the forks of Crooked Creek ; those 

 in the second group being rather of the Silverheels type, and those in the 

 Weber Grits either identical with or similar to the Lincoln Porphyry. The 

 number of these porphyry sheets is probably very much greater than 

 is shown on the map, which represents a generalized outline of the more 

 important bodies, deduced from observation made along three transverse 

 lines only in the area represented east of the Platte ; while in that portion 

 of the mountain which lies east of the boundary of the map the porphyry 

 bodies are, if anything, still more numerous. The swelling out of the strata, 

 produced by the intrusion of such considerable masses of eruptive rock, is 

 readily shown by the variations in the strike and dip. The steep north wall 

 of Silverheels, as seen from the summit of Hoosier pass for instance, shows 

 a fan-like arrangement of the easterly-dipping strata, which open out as it 

 were to the west. In other words, the section shows strata on the west foot 

 of the mountain, towards Beaver Creek Valley, dipping only 10 east; at 

 the summit of the peak the dip has increased to 17, while at the eastern 

 extremity it is 22, 25, and even 35. The divergence in strike produced 

 by the bowing-out of the strata is less evident on the map, owing to the 

 fact that at the point of greatest divergence the great elevation of Silver- 

 heels above the surrounding valleys brings the outcrops, as projected on a; 



