BY LEO A. COTTON. 519 



ascending waters were observed to enter the drive from the clay- 

 selvage. This phenomenon is probably the last phase in the 

 deposition of the ores. 



Comparison with other occurrences indicates the probability of 

 a genetic relationship between the silver-lead deposits and the 

 tin-deposits. Tlie tin-deposits of Cornwall, Germany, and Bolivia 

 have been thought to be closely related to the silver-lead deposits 

 in proximity to them. Again, Mr. Spurr has proposed a 

 magmatic extraction theory for ore-deposition, which is strongly 

 supported by the evidence of the sequence of deposition con- 

 tained in this paper. It is suggested that the Borali Creek 

 deposits liave been formed later tlian the tin-deposit'!, by deposi- 

 tion from higlily aqueous and siliceous magniatic extractions con- 

 taining relatively large amounts of metallic sulphides. 



Conclusion. 



In conclusion, it may he said that the genesis of the ore- 

 deposits indicates — 



(1) Permanence of the ore-body at much greater depth than the 

 limits of mining can attain. 



(2) A gradual increase, with depth, in arsenical pyrites, zitc- 

 blende, and possibly stannite, though, from the uniformity of the 

 lode, as already known, this probably takes place so gradually as 

 not to affect very appreciably the economic value of the deposits. 



(3) The probable permanence of the shoot in which the ascend- 

 ing waters were discovered in the Conrad Lode. 



It is not too much to hope that, in the near future, the 

 metallurgical difficulties in dealing with .so complex an ore may 

 be solved, and that this mine will take rank amongst the most 

 valuable of this State's mineral assets. 



EXPLANATION OF PLATES XV.-XVL 



Plate XV. 



Flg.l. — Photo, of Borah Creek, showing how the line of lode corresponds 

 with the Creek; and also showing the eiJeet of the large faults 

 upon the topography. 



