236 



Notice of Messrs. Foster and Whitnetfs Report 



The annexed is a section of the gangne 

 of a vein on the southeast quarter of section 

 10, township 60, range 39, Isle Royale: 



1. Laumonite, half an inch. 



2. Prehnite; with native copper, two 



inches. 



3. Clay, probably decomposed chlorite, 



one inch. 



This vein appears to have been subjected to three successive 



openings. 



The east vein of the Northwest Company exhibits two combs : 

 that attached to the foot-wall, six inches in width, is composed 

 of calc-spar with little copper; that attached to the hanging- 

 wall, twelve inches in width, consists of chlorite, quartz, and 



3 



We 



ppe 



.„ ^ ^.. .„ the chapter on 



mines, and ihey may be referred to in the further illustration of 

 the structure of the veins of this region. 



In the Cliff vein, there are two combs — that attached to the 

 foot-wall containing most of the masses, while the other carri^ 



The sheets of native copper, as a general 



copper 



thing, though not invariably, occupy the foot-wall of the vein 



Where crystals occur investing the walls, with their faces op- 

 posite, whether separated or interlocked, they atfoid strong pre- 

 sumptive evidence of the original width of the fissure. 



The Prince vein, Canada shore, affords a beautiful illustration 

 of this. The vein on Spar island is about fourteen feet in width, 

 the walls being invested with amethystine quartz, with the faces 

 turned outwards, occupying two feet in width, while the inter- 

 mediate space is filled in for the most part with calc-spar and 



pyntous copper. 

 It is difficult 



to determine the order in which the materials 



composing the matrix of veins were deposited. In some cases 

 the earthy substances were deposited before the metallic, and in 

 others it is evident that copper existed in the fissures before the 

 process of filling was complete. It is probable, however, that 

 the copper was formed at different times. 

 ^At the Copper Falls mine, for example, we find small specks 



enclosed in obtuse rhombohedral crystals of calc-spar, 



copper 



copper 



crystals of analcime and calc-spar, taking the form of the faces 

 of the crystals, every line and wave being faithfully represented, 

 as in the electrotype process. The copper often appears in arbo- 

 rescent forms, invested with calc-spar. 



The Prince mine affords specimens of dog-tooth spar, studded 

 with minute crystals of bi-sulphuret of copper, while the vitre- 

 ous copper is often enclosed in a matrix of carbonate of lime. 



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