MINES OUTSIDE THE LEADVILLE DISTRICT. 531 



ribbed structure, characteristic of the Blue Limestone horizon, very beauti- 

 fully developed. 



On the ridge between Spring Valley and Horseshoe gulch the Mudsill 

 claim has found galena at the same horizon, forming a contact deposit between 

 the darker and lighter limestones. To the east of this the Little Christine 

 has developed small veins of galena in the porphyry overlying the lime- 

 stone. On the eastern slopes of the range soi;th of Horseshoe gulch, as 

 well as on Sheep Mountain ridge, the contact of Blue Limestone and White 

 Porphyrj' has been but little prospected, and, although no considerable ore 

 bodies have yet been discovered in this portion, there is a fair probability 

 that more systematic search will yet develop them. Sheep Mountain being 

 a most especially promising locality. 



CREST OF THE MOSQUITO RANGE. 



A great deal of prospecting has been done along the very crest of the 

 Mosquito range, the bare, precipitous, and often almost inaccessible slopes 

 of high mountains seeming to offer especial attractions to the hardy pros- 

 pector. This may be, in part at least, explained by the fact that in these 

 elevated regions the rock surfaces are generally exposed and swept clean of 

 obscuring soil and other surface accumulations, and therefore the "indica- 

 tions " which they follow, such as a staining of iron oxide or of carbonate 

 or of silicate of copper, arc more readily seen than in the lower country, 

 whei'e, when found, ore is likely to be more remunerative. It seems hardly 

 necessary to say that the idea that prevails among some prospectors, and 

 to which credence is given even by some educated persons, that rich ore 

 bodies are more frequent near mountain-tops, has no basis of geological 

 evidence to support it. But few mines have been actually worked at the 

 crest of the range, and these only intermittently, which is hardly surprising 

 when one considers that it is frozen up nine months in the year. 



At the head of Mosquito gulch, and just west of the London fault, the 

 New York mine is said to hfive developed considerable rich ore at the con- 

 tact of the Blue Limestone with a small overlying sheet of White Porphyry 

 of local occurrence. 



