646 C. IE NEVE FOSTER ON THE GREAT FLAT LODE 



In many places the Great Flat Lode contains a good deal of chlo- 

 rite, some iron-pyrites, and kaolin. Occasion aly kaolin fills up 

 vughs or cavities in the quartz- veins. 



There is no wall or plane of separation between the lode and the 

 capel, nor between the capel and the granite ; the passage is gradual. 

 The granite near the capel is frequently soft, from the orthoclase 

 being wholly or partly kaolinized. 



Wheal Grenville. — On account of its dip, the Great Flat Lode leaves 

 South Condurrow at the 93-fathoms level and enters Wheal Gren- 

 ville, where it has been worked on between the 130 and 160 fathoms 

 levels. Comparatively little work has yet been done here; the 

 course of the lode in the present workings is from 27° to 32° N. of E., 

 and the dip about 30° S. The leader varies from a mere joint to 2 

 feet in thickness, and on each side you have a " capelly " lode. Of this, 

 about 2 feet are taken on each side with 1*6 per cent. (36 lbs. per 

 ton of stuff) tin-ore, whilst capels are left standing 1 to 8 feet thick, 

 containing j to 1 per cent, tin-ore, which is rock that cannot be 

 worked with profit at present prices. 



I may be fairly asked to bring forward proofs that the lode and 

 capel are really schorl-rock ; for they differ very decidedly from a 

 typical granular schorl-rock, such as that of Eoche, for instance. I 

 was first led to infer the presence of schorl from finding evidence of 

 much boron while examining the lode-rock by the blowpipe (' Mine- 

 ralogical Magazine,' vol. i. 1877, p. 75) ; and subsequent tests revealed 

 the existence of fluorine, silicon, aluminium, potassium, and iron, 

 all of which are component elements of tourmaline. 



I then called the microscope to my aid. Thanks to the kindness 

 of Mr. J. H. Collins, who readily afforded me every assistance, I 

 have been able to examine some sections of lode and capel prepared 

 for me by Mr. J. B. Jordan. When magnified 300 diameters the 

 capel is seen to consist of a felted mass of minute crystals imbedded 

 in a basis of quartz. In places you observe spots and patches where 

 the quartz predominates ; some of these spots are oval and rounded, 

 others angular, and a few that are hexagonal in section naturally 

 suggest the former presence of felspar. Mr. Frank Rutley, who 

 examined several slides for me, agrees with me in this opinion. 



The rock forming the lode presents a similar matted mass of fine 

 needles in a ground-mass of quartz, with granules of cassiterite 

 scattered through it or arranged in little strings and veins. The 

 needle-like crystals are very like some larger ones in specimens of 

 undoubted schorl-rock in Mr. Collins's possession. The microscopical 

 evidence is in favour of the opinion forced on me by the blowpipe 

 reactions, which is thoroughly in accordance with the views so ably 

 brought forward thirty-six years ago by Prof. Daubree with regard 

 to the minerals associated with tin-ore*. 



* "Memoire sur le gisement, la constitution, et lorigine des amas de minerai 

 d'etain." Annales des Mines, 3me serie, tome xx. 1841, p. 65. 



