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nately prospectors as a class, rot only of asbestus properties but of 

 other minerals as well, are not sufficiently well informed as to such 

 conditions. Many arc led by what they have observed in connection 

 with mines in certain other areas, such as for instance in the case of 

 the Cornish miner, who measures everything in i Cornish half bushel. 

 Whereas the truth is that the profitable or economical development of 

 minerals very frequently depends upon the presence of local phenomena 

 or conditions which have affected certain limited areas only of the earth's 

 .surface or crust. Just what the conditions have been in the past by 

 which the serpentine areas of Thetford and Black Lake have become 

 so impregnated with asbestus veins of great purity and large size, 

 whiie the areas a short distance to the east or west should be almost 

 devoid of asbestifoim mineral, cannot yet be conclusively settled. Lt 

 is possible that the presence of the large intrusive masses of granulite, 

 which are of more recent date than the serpentine, may have had some 

 effect in this direction, but in that case we should expect to tind at 

 Black Lake, where these granitic masses are the most abundant, the 

 richest deposits ot asbestus. On the contrary, however, it is found 

 that the largest and most important veins are found at Thetford where 

 the granitic masses are comparatively small and generally confine^ 

 to narrow dykes ; for while the serpentine of this area is, according 

 to the best testimony on the subject, due to an alteration of igneous or 

 dioritic rocks, we can scarcely suppose that the asbestus itself is of 

 igneous origin. While, therefore, the reason why the Thetford areas 

 are the most productive of tine asbestus fibre has not yet been satis- 

 factorily ascertained, we have been able to learn some facts from the 

 study of these Thetford mines, which are of value to guide the pro- 

 spector or the scientific explorer in the search for other deposits. 



Since the asbestus veins occur throughout the mass of the rock and 

 come directly to the surface where exposed, as in the hill at Thetford 

 mines and the great escarpment to the south east of Black Lake sta- 

 tion, the mining of the mineral does not follow the methods which are 

 usually employed in the working of other mines, viz., by underground 

 slopes and levels connected with the surface by shafts, but is simply 

 open quarry work, the entire rock being removed, broken up and the 

 veins of asbestus separated by hand cobbing, in so far as the size of the 



