Geological Society of London. 137 



rock from 4 to 15 feet wide; tMs contains from-1 to 3 per cent, of 

 cassiterite, in little grains, or in strings or veins. Schorl rock, very 

 poor in tin (locally called ca-pel or greyback), separates the lode 

 from the surrounding granite or killas, but passes on one side into 

 the lode, and on the other into the granite or killas, so that no ivall 

 is recognizable. From these characters the author inferred that the 

 lode and the capel are merely altered rocks, the fissure now occupied 

 by the leader having served to bring up vapours or solutions which 

 have entirely changed the rocks on both sides of it. In support 

 of his opinion, the author adduced other instances of the change of 

 both granite and killas into schorl rock ; and further stated that, 

 both at South Condurrow and Wheal Grenville, he has found in the 

 schorl rock cavities as large as a pea, agreeing in form with crystals 

 of orthoclase felspar. 



2. " On some Tin-mines in the Parish of Wendron, Cornwall." 

 By Dr. C. Le Neve Foster, B.A., F.G.S. 



The mines described in this paper are called Balmynheer, the 

 Lovell, and South Wendron. In the former the stanniferous deposit 

 consists of a large irregular mass of rock 30-50 feet thick ; its 

 dip is N., at an angle of about 30°, and its strike E. 32° N., along 

 which it has been traced for 36 fathoms. The tinny rock is separated 

 from the granite above by a slide dr vein of white clay, with a 

 little quartz and mica, about 6 inches thick, but passes insensibly 

 into the granite below. At the Lovell Mine there are two lodes, 

 north and south, the former striking from 37° to 45° N. of E. and 

 dipping N.W. at an angle of about 70°, the latter running E. 48° N. 

 and dipping N.N.W. about 60°, so that the two lodes unite in going 

 eastward and in depth. The lode is separated on one or both sides 

 from the adjoining granite by a rock locally known as '' cab," 6-12 

 inches thick, composed of quartz, mica, gilbertite, chlorite, iron 

 pyrites, copper pyrites, and a little schorl. The lode itself shows 

 joints which are mere planes of division in the rock, and usually 

 have the same strike and dip ; divergent joints also occur, and where 

 these traverse the granite, they carry with them a little tin-stuff for 

 some distance. The South Wendron Mine is worked in an irregu- 

 larly cylindroid pipe of tinny rock, merging gradually on all sides 

 into the granite ; the shorter axis of its oval section is about 10 feet, 

 while the longer axis varies from 20 to 60 feet. It dips at an angle 

 of 49° in a direction N. 25° W. The stanniferous rock in these mines 

 is essentially a mixture of quartz, chlorite, gilbertite, iron pyrites, 

 and tin-ore, with zinc-blende in some cases, and usually some mica ; 

 fine needles of tourmaline occur in the cavities which it incloses. 

 In the South Wendron Mine the southern part of the pipe is some- 

 times very granite-like in appearance, consisting of pink orthoclase 

 crystals imbedded in a mass of quartz, chlorite, mica, and iron 

 pyrites, with a little copper pyrites, fluor, and tin-ore. One specimen 

 is a true stanniferous granite. These characters lead the author to 

 the same conclusion he has arrived at in the case of the Great Flat 

 Lode, namely, that these tin dejDOsits consist entirely of altered 

 granite, and are not ordinary mineral veins ; they have no walls, 



