462 GEOLOGY AND MINING INDUSTRY OF LEADVILLB. 



Porphyry, as are the transverse sheets of Gray Porphyry already noticed, 

 and like them its influence has been favorable to the deposition of rich ore. 

 It should not, however, be regarded as a dike cutting through the ore 

 bodies, since it was evidently intruded before ore deposition commenced. 

 Its exact relations to the original ore bodies are now difficult to define, for 

 these were probably deposited in the form of sulphurets in a much larger 

 proportion of unreplaced limestone than now exists, and the secondary 

 action of oxidation, which has been going on ever since, has evidently in- 

 creased the volume of vein material and reduced that of the unreplaced 

 limestone. The probability is that, as in cutting across the formation this 

 body probably interrupted some of the natural water channels along the 

 contact planes of different rock formations, it caused a partial stagnation of 

 the ore currents in its vicinity and thus favored precipitation and replace- 

 ment action there. 



The ore bodies are continuous around its western end from the Trian- 

 gle workings to Chrysolite No. 4, and it is probable that its western limit is 

 not far from that indicated by its outcrop on the map, as otherwise it would 

 have been cut by some of the drifts in this portion of the mine, which, 

 owing to the basining-up of the formation here, reach lower horizons than 

 elsewhere. The ore bodies are also practically continuous across the line 

 of the dike along the Carboniferous-Little Chief line, but here the dike is 

 proved to exist under these ore bodies by drifts at lower levels, and the in- 

 ference, therefore, is that, as the dike did not extend up to the upper sur- 

 face of the Blue Limestone, ore deposition went on uninterruptedly across 

 this break in its upper line. It was just to the north of the dike, in the 

 Little Chief ground, that the thickest body of pay ore was found. The ore 

 body in the extreme southeastern portion of the Carboniferous claim was also 

 very thick; but, being among the earlier discoveries, the workings had 

 caved at the time of visit and could not be examined; 12 feet of lime-sand 

 and 24 feet of ore are said to have been cut by this shaft. 



New Discovery. The New Discovery claim adjoins the Carboniferous and 

 Chrysolite on the south and the Vulture on the east, and geographically 

 forms part of the ground just described, though it belongs to the Little 

 Pittsburgh Mining Company, the claim of that name lying entirely to the 



