ORIGIN AND DEVELOPMENT OE ORE-DEPOSITS. 127 



Opening from this on the east side is another excavation, about 

 100 feet long, 30 wide, and 20 deep. The hill consists of 

 granite, the felspar of which is in parts completely decomposed, 

 forming masses of china clay, interspersed with grains of quartz 

 and flakes of mica" (carclazyte). The main pit is crossed by a 

 large caunter tin lode, or rather a tin-bearing belt of ground 

 having no distinct walls. This runs nearly N.E., and dips steeply 

 N.W., it consists chiefly of schorl and quartz, but contains on an 

 average from 6 to 8 lbs. of tin to the ton of stuff. It is crossed 

 by another belt of very similar character, running nearly N.S. ; 

 this is known as the cross-course, although it in no way resembles 

 the ordinary cross-courses of the West of England ; it appears 

 slightly to heave the "lode" however, and itself contains tin 

 (especially) near the intersection, sometimes as much as 20 lbs. 

 to the ton. 



Besides the " lode " and the " cross-course," a great number 

 of smaller lodes and branches traverse the pit in almost every 

 direction, many of them coming together about the centre of the 

 pit, a little to the east of the point of intersection of the two 

 greater masses. At some of the intersections rich bunches occur, 

 some yielding 50 or even 60 per cent, of oxide of tin, and from 

 one such bunch 17 tons of tin were got out about the year 1870.^ 

 From 1872 to 1874 the average produce of the stuff treated was 

 about 10 lbs. of tin per ton of stuff crushed, or about 7 lbs. per 

 ton of stuff broken. A very careful and economical mode of 

 working was adopted, but it was on too small a scale, rarely 

 exceeding 150 toQS per week, and as the stuff was extremely hard, 

 the stamps were worked by steam, and even the water for dressing 

 had to be pumped by steam power, the mine barely " paid cost,'' 

 even when black tin was selling at £90 per ton, and when the 

 price fell to a little over £60, the works were abandoned. Still, 

 taking into account the chances of meeting with occasional rich 

 bunches, I think the abandonment was certainly premature, f 



* Eeport, Miners' Assoc, 1872, p. 67, published 1873. See also " The Hens- 

 barrow Granite District, pp. 40-47. 



f The interesting occurrence at this mine of porphyritically embedded pseudo- 

 morphous crystals of schorl, quartz, oxide of tin, and of mixtures of two or three 

 of these together, in the form of felspars, and also the occurrence in cavities of the 

 rare mineral achroite was described by the writer in the year 1876, in the Mineral- 

 ogical Magazine, Vol. 1, 1876, p. 55, 



