162 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



strike of the formations, N. 10° to 20° W. This fault has been assumed, 

 therefore, to follow the bed of the gulch, and probably connects the Sher- 

 man with the London fault ; its line is not given on the map, as it would be 

 concealed by the Quaternary beds indicated in the bed of the gulch. The 

 course of the gulch in this extent, which is unusually straight, has probably 

 been determined by this fault. 



The structure of this Sheep Mountain ridge, as deduced from careful 

 observations made along its surface, is shown in Section G, Atlas Sheet 

 IX. Of the White Limestone and Lower Quartzite, which are only exposed 

 in the amphitheater south of the Horseshoe, measurements were not made, 

 since those obtained from the exposures in the Horseshoe itself correspond 

 with the thickness obtained elsewhere. The bod}- of White Porphyry, which 

 sweeps up at an angle of 20° opposite the opening of the amphitheater, has 

 here a thickness of nearly two hundred feet, and shows a certain tendency to 

 columnar structure at right angles to the bedding. The beds immediately 

 above the White Porphyry contain a large proportion of shales, which, being 

 easily disintegrated, show but few outcrops, the space occupied by them 

 forming a saddle in the ridge. The thickness from the White Porphyry 

 up to the more persistent sandstones and grits of the Weber series, which 

 would correspond to the Weber Shale division, is here estimated at from 

 two hundred to three hundred feet. The beds observed are as follows : 

 Directly above the White Porphyry is a bed of black carbonaceous shales ; 

 from one hundi-ed to one hundred and fifty feet above it is an outcrop of 

 dark, impure limestone, from which were obtained a large number of fossils, 

 amons; which the following were recognized: 



Chonetes granuUfcra. 



Productus cora. 



Productus nodosus (variety of Pro- 



diictus com). 

 Productus sem ireliculai us. 

 MijaJina pcrattenuata. 



Fragment oi Pinna, sp. 

 Fragment of Aviculopecten. 

 PJiillipsia, sp. 

 PhUlipsia major. 

 Fragment of lAngula, sp. 



About fifty feet above this there is a bed of black shales, from which 

 were obtained impressions of Lingida mi/tiloides, the same form which is 

 so abundant directly above the Blue Limestone near Leadville. For 

 about three-fourths of a mile eastward along the crest of the rido-e the 



