Vol. 4] Lawson. — The Robinson. Mining District. 351 



tals of ehiastolite. The ground mass of the rock is murky and 

 much obscured by particles of carbonaceous matter. Through 

 this are disseminated small flakes of brown biotite. The ehias- 

 tolite, in beautifully idiomorphic crystals with geometrically dis- 

 posed carbonaceous inclusions, lies in this matrix. The sections 

 are square, oblong and rhombic, and the carbon is arranged in 

 the usual way so characteristic of ehiastolite. The size of these 

 chiastolites is generally about .5 mm. in longest dimension. The 

 discovery of such pronounced evidence of thermal metamor- 

 phism under such conditions is most interesting as indicating 

 that no greater time is required to effect such changes than is 

 required for a magma to solidify as a glass — a period which is 

 generally conceded to be quite short. 



OTHER METALLIFEROUS DEPOSITS. 



Before the Robinson Mining district became known as a pros- 

 pective copper camp, various attempts had been made to mine 

 lead-silver, and gold ores. Up to the present these attempts can 

 not be said to have been successful in the sense of having led 

 to profitable mining operations. But a considerable amount of 

 capital has been sunk in the district in gold mines and an un- 

 certain amount of selected ore has been shipped out from the 

 lead-silver mines. 



The writer has made no special study of these deposits and 

 cannot, therefore, undertake their discussion here. It is de- 

 sired, however, to call attention to certain features of these de- 

 posits, particularly as regards their relation to the ore-bearing 

 porphyry. The lead-silver deposits form a fairly well defined 

 belt confined to the Ruth limestone and lying to the north of 

 ore-bearing porphyry and Lane Valley. The gold deposits occur 

 in various Palaeozoic formations, particularly the Ruth lime- 

 stone and the White Pine shale, and are distributed in a belt 

 on the south side of the ore-bearing porphyry and Lane Valley 

 although just beyond the area mapped there are some gold pros- 

 pects on north of Lane Valley. This general distribution of 

 the two kinds of deposits appears to the writer to be significant 

 of a genetic relationship with the same porphyry which has 

 given rise to the copper ore. In the vicinity of the Ruth Mine 



