STRUCTURE OF FRYER HILL. 489 



the ridge in the main Stray Horse gulch there is some indication of a 

 westerly dip beyond a slight anticlinal fold. It is unfortunate that no 

 more exact information could be obtained with regard to it at this locality, 

 as upon the verification of the westerly dip depends in large degree the 

 probability of the occurrence of the ore horizon under the city of Leadville. 

 Its existence at the west end of Fryer Hill is, however, definitely ascer- 

 tained, and has been shown to be extremely probable along the west base 

 of Carbonate Hill, which lends force to the supposition that it also occurs 

 at this intermediate point. 



RESUME. 



From the above descriptions it is apparent that, in spite of the greater 

 complications of structure, the series of rock formations on this hill is 

 essentially the same as that on Carbonate and Iron Hills, and that the 

 processes of ore deposition have been essentially the same, though the 

 secondary alteration of the deposits, which may be mainly ascribed to the 

 action of surface waters, has been carried much farther. The Cambrian, 

 Silurian, and Lower Carboniferous horizons are found in their normal posi- 

 tions, the Parting Quartzite being here, as elsewhere, of somewhat variable 

 thickness, and the Blue Limestone horizon, which is often split up into 

 several portions and entirely replaced by vein material, being then defined 

 by this quartzite below and by the micaceous sandstone or quartzite of the 

 Weber Shales above. 



The intrusions of porphyry are more extensive and more varied and 

 irregular in form. Above the normal sheet of White Porphyry, which 

 here as there overlies the ore horizon, with detached portions of the Weber 

 Shales left between, is the main sheet of Gray Porphyry, in great measure 

 eroded off, which does not occur on the other hills. In addition to this, 

 there is the second or lower sheet of White Porphyry, occurring generally 

 at the base of the Blue Limestone horizon, but in some places cutting up 

 across its lower portion and in others cutting down below the Parting Quartz- 

 ite; further, there are ramifying offshoots from this lower White Porphyry, 

 which have locally divided the Blue Limestone horizon into several dif- 

 ferent portions. Of later Gray Porphyry intrusions, there is the larger 



