BY W. F. PETTERD, C.M.Z.S. 37 



minerals usually occurring with it. It is from this dis- 

 trict that many remarkably well-developed tin crystals 

 are obtained. They are frequently found studding the 

 walls of fissures and vughs in the lodestone. The veins 

 and impregnations are often extremely irregular, varying 

 in width and length, and even in extension to depth. 

 In the Ben Lomond district pipes and floors have occurred 

 with the tin ore occasionally in fair proportion. The 

 Great Republic Mine is a fair example of the first, con- 

 taining remarkably fine well-formed crystals of cassiterite 

 with the companion minerals fluorite and pyrites. The 

 floors are very similar to like occurrences in Cornwall, viz., 

 a narrow crack, now often filled with chalcedony. That 

 apparently served as a channel for the ascending vapours, 

 which probably acting on the adjacent rock in favourable 

 positions deposited the tin ore, which now appears as floors 

 of limited extent, but often extremely high in tin con- 

 tents. 



The other tin-mining districts are those of Heemskirk, 

 North-East Dundas, Cox's Bight in the extreme south, 

 Mt. Ramsay, Bell Mount, and a few outlying localities. 



The general characteristics of cassiterite as occurring in 

 this island may be thus summarised: — In colour this min- 

 eral varies to a remarkable degree; it is commonly black 

 and in various shades of brown, but is sometimes almost 

 colourless, red, yellow (pale and dark), white, grey, and 

 not rarely variegated. In structure it may be compact, 

 fibrous, nodular, radiating, or crystalline. According to 

 colour or structure its varied forms are termed by the 

 miners black tin, ruby, resin, wood, shot-holed, mahogany, 

 and other local appellations. Alluvial tin is generally 

 much waterworn or rolled, but in many cases the crystals 

 are but little abraded; it is usually opaque, but is occa- 

 sionally translucent to almost clear transparent. 

 Examples of this latter variety, when cut into gemstones, 

 display a brilliancy second only, in their high refractive 

 index, to the diamond. The adamantine lustre of fresh 

 crystals, coloured or black, is very pronounced, and the eye 

 is attracted by the splendent faces. As a rule stream or 

 alluvial tin — as with gold — is commonly richer than that 

 derived from its matrix or lodes. This is probably caused 

 by the outer crust being abraded, the richer central por- 

 tion remaining uncontaminated by any incrustation of 

 foreign matter. 



At North-East Dundas cassiterite is reported to occur 

 under exceptional conditions in association and inter- 



