SUMMARY. 187 



In the mines on Ruby Hill, southeast of the "compromise line," the ore 

 bodies usually occur connected with the quartzite, but in the Richmond 

 and Albion they are almost always far removed from it. 



SOURCE OF THE ORE. 



Possible sources of the ore— The possible sources of the ore are a deposition in 

 small particles with the limestone, the ore being afterwards segregated into 

 nearly isolated bodies either by chemical or mechanical action; a segrega- 

 tion of the ore in the limestone from the country rock on either side of it; 

 and a deposition from solutions which came from below. 



Precious metais in the different roC ks._Several series of assays made with extraor- 

 dinary precautions show that the stratified limestone contains only the mi- 

 nutest traces of silver, while the mineral limestone, especially where it is 

 iron-stained, contains a number of cents per ton. The silver contents, how- 

 ever, on the whole, diminishes as the distance from the ore bodies increases, 

 and nowhere answers to the composition which the rock must have pos- 

 sessed had the ore bodies been derived from it. The trace of silver in 

 the limestone is an impregnation from the ore bodies. The shale never 

 carries more than a trace of silver and gold, and the quartzite could not 

 have furnished the material of the ore bodies. There are also good struct- 

 ural reasons for believing that the ore cannot have been formed by segre- 

 gation from the surrounding rocks. Neither do the examinations furnish 

 any reasons for believing that either the granite or the rhyolite yielded the 

 metallic compounds of the ore bodies. 



Quartz-porphyry as a source of the ore.— Oil the Other hand, the qUartZ-pOiph VI V 



proves to contain silver, gold, and lead in no inconsiderable quantities, and 

 has manifestly been subjected to chemical action involving the solution ot 

 a portion of its metallic contents. Of this the decomposition of the rock, 

 combined with a notable concentration of silver and gold in the pyrite 

 (which is of secondary origin), are evidences. While the quartz-porphyry 

 appears on the surface only in a small area, it is entirely possible that the 

 mass underlies a great part of the district, and that it may have yielded the 

 ore which was deposited in the limestone. This, however, is uncertain, 

 while it is tolerably safe to say that of all the rocks which appear at the 



