132 OEIGIN AND DEVELOPMENT OF ORE-DEPOSITS. 



of the mass in which the tin is thus abundantly dispersed (over 



1 per cent, as it appears), the grains appear of a crj'stalline 

 transparency, and so equal in size and regularly distributed as 

 to form as it were one of the constituent parts of the porphyry,"* 



Wheal Jennings. This mine is situated in the parish of 

 Gwinear, and was formerly worked under the name of Parbola. 

 Mr. Seymour, who gave a very good illustrated description of the 

 mine in the year 1876, f does not regard it as a true stockwork 

 *' because the tin-bearing branches follow (mainly) one direction," 

 but as we have seen this is the case at Mulberry and many other 

 recognized stockworks. The elvan traverses a somewhat soft 

 killas, and contains many small veins of tin which mostly pass 

 across it from killas to killas, others falling into them in their 

 course. Some pass into the killas after traversing the elvan. 

 The elvan itself contains disseminated grains of tin, forming 

 masses known as " grey-tin," also angular masses of " granite." 

 Mr. Seymour regards the tin veins as shrinkage-fissures sub- 

 sequently filled by means of stanniferous solutions which arose 

 through the fissured mass, " where the mass of rock was in a 

 greater degree porous, the emanations penetrated into and 

 impregnated the adjacent elvan, thus forming the deposits of 

 so-called " grey-tin. ":j: 



Belowda Hill. A large elvan cuts through the granite at 

 Belowda Hill, and both rocks are found to be stanniferous in an 

 open-cutting which has been worked at intervals on a considerable 

 scale. Dr. Foster wrote a short note on the works here, which 

 appeared, in the year 1875, in our Journal. He stated that the 

 "lode" was 40 feet wide at the time he saw it, and that the stannif- 

 erous belt so-called was traversed by numerous tin branches from 



2 inches to 6 inches wide, which carried quartz, schorl and tin — 

 some tin being found in the intermediate masses of rock also, 

 in some cases as pseudomorphs after felspar. Ho states that 

 the general produce of the stuff was one-half per cent.§ In 

 1880 I superintended the works here for a short time, during 

 which a battery of stamps was set up and several hundred tons 



* John Hawkins, Trans. Roy. Geol. Soc, Corn., Vol. i, p. 140. 



f Trans. Roy. Geol. Soc, Corn., ix, p.p. 185, 195, 



X Ibid. 



§ Journ. R.I.C., V, p. 213. 



