es 
in all three principal ingredients of Cornish granite.* The granite 
of Cornwall is, for the most part, coarse-grained, but in this re- 
spect it differs considerably in different places; for example, that 
of the Saint Just and Saint Ives districts has a much coarser 
texture than any other, whilst at Tregoning and Godolphin it is 
usually finer. Moreover the coarse-grained rock is often traversed 
by veins of a like substance but of finer texture. Sometimes also 
isolated spheroids of schorl rock are embedded in it. Two series 
of joints, which intersect nearly at right-angles, divide the granite 
into rude quadrangles; others, of intermediate directions, sub- 
divide it into triangles ; and a bedding—approximating, in various 
places, to the contour of the surfacet—often gives the rock a 
somewhat gneissose character. 
The slate, in a general way, rests on the granite at an angle 
of perhaps 20°-45°;{ but in some cases the junction is nearly 
vertical ;§ and in other the rocks interlie near their boundaries. || 
Not uncommonly, however, just on the line of junction, the granite 
becomes extremely fine-grained ; the slate, on the other hand is 
massive, and can be distinguished from the granite, merely by its 
darker colour. Veins of granite frequently penetrate the slate, 
and masses of either rock are sometimes embedded in the other.** 
One district, indeed,—a distant one from any yet known body of 
granite,—affords numerous rude granitic spheroids completely 
isolated in the slate.tt It is by no means easy to describe the mi- 
neralogical composition of the slates, as the proportions of their 
various ingredients are seldom constant over any considerable 
tract. It may, perhaps, be stated that felspar, chlorite, mica, schorl 
* Sorby, Quarterly Journal of the Geological Society, xiv.; pp. 488, 
500; Figs. 111, 112, 118, 114, 115, 117, 118, 119, 120. 
+ Mac Culloch, Geol: Trans: ii., p. 71. Boase, Cornwall Geol: Trans: 
iv., p. 366. Hnys, London and Edinburgh Phil: Mag: ii., p. 322. Whitley, 
Reports of the Royal Institution of Cornwall, xxxii., p. 31. Henwood, Corn- 
wall Geol: Trans: v., p. 171; viii., p. 672. 
+ Thomas, (R.), Survey of the Mining District from Chasewater to Cam- 
borne, p. 10. Henwood, Cornwall Geol: Trans: v., p. 151. Thomas, (C.), 
Remarks on the Geology of Cornwall and Devon, p. 19. 
§ Henwood, Cornwall Geol: Trans: v., p. 151. 
|| De Lue, Geological Travels} iii., p. 293. Phillips, (W.), Geol: Trans: 
O.8., ii., p. 153, Pl. vii., Fig. 8. Thomas, (R.), Survey, p 10. Henwood, 
Cornwall Geol: Trans: v., p. 148; viii., p. 658. Webb and Geach, History 
and Progress of Mining, &c., p. 67. 
q Davy, Cornwall Geol: Trans: i., p. 20. Forbes, Ibid ii., p. 258. 
Carne, Ibid ii., p. 326. Edmonds, Ibid iii., p. 332. Boase, Ibid iv., p. 391. 
Henwood, Ibid v., pp. 150-151. 
** Forbes, Ibid ii., pp. 254, 256. 
++ Henwood, v., pp. 36, 72, 157. Salmon, Quarterly Journal of the 
Geological Society of London, xvii., pp. 517-522. 
