On some of the Stochvorks of Cornwall. 235 



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 east- 

 ward 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 irregularly 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 di- 

 rection "N. 25° W. The stanniferous rock in these mines is essen- 

 tially 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 occnr in the cavities which it encloses. In the 

 South-Wendron Mine the southern part of the pipe is sometimes 

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

 tals 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 deposits consist entirely of altered granite, and 

 are not ordinary mineral veins : they have no walls, but the stannife- 

 rous rock passes gradually into granite ; and they show no signs of 

 banded structure due to the successive deposition of minerals. The 

 highly granitic character of part of the South-Wendron tin deposit is 

 strongly confirmatory of this view, which is further supported by the 

 occurrence, in the dark mass of the so-called lode at the Lovell, of 

 pseudomorphs of quartz after orthoclase containing a little cassiterite. 



3. "On some of the Stockworks of Cornwall." By Dr. C. Le 

 Neve Poster, B.A., F.G.S. 



The author commenced by explaining that the term " Stockwork " 

 had been derived from the German StocJcwerck, meaning " Story- 

 work," in allusion to the method of working in steps or stories 

 in open workings, originally adopted for such deposits. Their being 

 worked in open quarries affords a good opportunity of studying tho 

 mode of occurrence of tin ; and many of them are interesting on 

 account of the small percentage of tin which will cover all expenses. 

 Thus, in the Wheal-Prosper Mine, the average amount of oxide of 

 tin obtained per ton of stuff is not more than 3 lb., worth, at the 

 present price of " black tin," 4|d. per lb. ; so that the ground as it 

 stands is only worth 13|d. per ton. The mine can be worked 

 without loss, on account of the softness of the rock and the large size 



