640 C. LE NEVE FOSTER ON THE GREAT FLAT LODE 



37. On the Great Plat Lode south of Redruth and Camborne, 

 and on some other Tin-deposits formed by the Alteration of 

 Granite. By C. Le Neve Foster, Esq., B.A., D.Sc, F.G.S. 

 (Read January 9, 1878.) 



[Plate XXX.] 



Few persons who have visited West Cornwall can have failed to 

 notice the marked hill known as Carn Brea, about a mile S.W. of 

 Redruth. This hill forms part of a mass of granite about four miles 

 long, in a direction E. 30° N., generally about five furlongs wide, 

 but terminating both east and west in a long narrow tongue. The 

 granite is surrounded on all sides by the so-called killas or clay- 

 slate. To the north of the hill are numerous famous mines, such as 

 Dolcoath, Cook's Kitchen, Tincroft, and Carn Brea ; and to the south, 

 again, mining operations have been carried on to a considerable 

 extent. I propose to describe some of these latter workings, which 

 possibly form part of one great mineral vein stretching for more 

 than three miles from Perseverance Mine on the east to South 

 Tolcarne on the west. 



The accompanying plan and section (PL XXX.), which have kindly 

 been compiled for me from the originals by Mr. Thomas B. Provis, 

 Assoc. Inst.C.E., show the situation of the workings ; for the sake of 

 clearness levels on other lodes have been omitted. From a cursory in- 

 spection of the plan it would appear doubtful whether all the work- 

 ings belong to one and the same lode ; the West Wheal Frances 

 drivages, for instance, are not in a line with those at similar levels 

 to the E. and W. This shift of a portion of the lode to the south 

 may have been caused by north and south faults (cross courses), several 

 of which are known to exist ; however, the continuity or non-con- 

 tinuity of these deposits is not a question which affects the purpose 

 of my paper, the main object of which is to describe the occurrence 

 of the tin-ore and point out how the mineral repositories in question 

 differ from those which are included in the ordinary definition of 

 a lode or mineral vein. 



I propose to treat the subject under the following heads : — 



I. Description of the lode as seen at the various mines. 



II. Its probable mode of origin. 



III. Alteration of granite in other districts. 



IV. The definition of the term lode or mineral vein. 



V. Statistics of the output of tin-ore from the Great Flat Lode. 



I. Description of the Lode. 



Wheal Uny lies a little to the S.E. of Redruth Church, and is 

 entirely dependent on the Great Flat Lode. In the eastern part of 



