TRANSACTIONS OF TH E SUCTIONS. 71 



Tim Loral] mine is worked Upon two so-called lodes, which are irregular masses 

 of tLn-bearing rock, adjoining' certain joints running about N.E. and S.W. The rock 

 is made up of quartz, gilbertite, mica, zinc-blende, chlorite, iron-pyrites, and tinstone. 



Smith Wendron is remarkable for a pipe of somewhat similar rock. 



The author supposed that the tin-bearing rock is an altered granite, and brought 

 forward in support of his argument the facts — 1st, that pseudomorphs of quartz and 

 of gilbertite after orthoclase are found at the Lovell mine ; and 2ndly, that there is 

 always a gradual passage from the tin-bearing rock into the granite, (See Quart. 

 Journ. Geol. Soc. vol. xxxiv. 1878, Aug.) 



On the Great Flat Lode south of Redruth and Camborne. 

 Bg C. Le Neve Foster, B.A., D.Sc, F.O.S. 



In this paper the author described an important tin-lode which is wrought in 

 various places for a distance of 3i miles, at Wheal Uny, West Basset, &c. 



In some places it occurs (for instance, at Wheal Uny) at the junction of the clay- 

 slate ( killas) and granite, but in other mines it lies entirely in granite. 



Its characteristics are — 



1. A leader or true fissure vein, generally only a few inches wide, and filled with 

 clay, fragments of the enclosing rocks, and tin- or copper-ores, dipping 30° to 50° S., 

 and striking from 20° to 45° N. of E. (true). " 



2. The lode, from 4 to 15 feet wide, on one or both sides of the leader, consisting 

 mainly of schorl-rock, containing grains and veins of tin-ore. It yields from 1 to 3 

 per cent, tin-ore. 



3. A capel, or non-stanniferous or slightly stanniferous schorl-rock, separating the 

 lode from the killas or granite. 



4. Absence of any wall or plane of separation between the lode and capel, or 

 between the capel and granite. 



The author said that all the appearances pointed to the fact that the lode and 

 oapel are merely altered granite. In confirmation of this view, he explained that he 

 bad found cavities in the lode resembling felspar crystals in shape, and probably left 

 by its removal ; furthermore the microscopic examination of the capel shows ap- 

 parent pseudomorphs of quartz after felspar. 



If it is admitted that the mass of the " Great Flat Lode" and its capels are altered 

 rocks once containing felspar, we are driven to conclude that that rock must once 

 have been granite, because of the gradual passage of the capel into granite. Sup- 

 posing this view to be correct, we must adopt a similar explanation in the case of 

 many of the important tin-lodes in Cornwall. 



The great mines north of Carn-Brea Hill, such as Dolcoath, Cook's Kitchen, some 

 of the Carn-Brea lodes, South Crofty, and East Pool, all furnish" tinstuff" more or 

 less similar to the stanniferous rock described above ; and the author ventured the 

 opinion that half of the tin-ore obtained in Cornwall is now derived from altered 

 granite. He contended that the typical tin-lode of Cornwall should no longer be 

 represented as the mere contents of what was once an open fissure, and asserted that 

 though fissures were necessary, their principal function was, not to serve as recep- 

 tacles for minerals, but to convey the fluids which changed the granite and deposited 

 the tin-ore in little minor cracks and pores of the altered rock. The large tin-lodes, 

 in the author's opinion are merely long tabular stockworks rather than ordinary 

 mineral veins. 



In the year 1876, 83,452 tons of tinstuff were produced from the Great Flat Lode, 

 yielding 1846 tons of clean tin-ore (black tin) , or more than \ of the total quantity 

 of tin-ore obtained from Cornwall. (See Quart. Journ. G. S. vol. xxxiv. 1878, Aug.) 



On the Geological Significance of the Boring at Messrs. Meux's Brewery, London. 

 Bg E. A. C. Godwin-Austen, F.B.S. 



A Short Slcekh on the Finding of Silurian Rods in Teesdale. 

 Bg W. Gunk, F.G.S. 



