XXV1 
unfavourable influence on the produce of lodes ; bodies (courses) of 
ore sometimes terminating abruptly at a joint.* The cleavage- 
planes of the slates are almost invariably contorted whenever the 
rock is quartzose; in such cases it is usually fissile, and the la- 
minee are highly inclined ; either of these conditions is accounted 
inauspicious. On the other hand, when the planes of cleavage 
are free from curvature and moderately inclined, and when the 
rock is of thick-lamellar structure, the Jodes which traverse it may 
hold out fair promise. The fissile slates are frequently hard ; 
whilst the thick-bedded varieties are usually much softer. 
For several years past the chief produce of two, almost ad- 
joining tin-mines of great importance has been obtained trom 
deposits,{ of which examples are yet unknown in other parts of 
Gorwalll They all anastomose with lodes ; and these, in the two 
most notable instances, bear 17°—25° S. ‘of EN. of W., one 
being nearly perpendicular, the other generally dipping S. At 
their contact with the lodes, to which these repositories are respec- 
tively united, one of them measures no more than a few inches in 
height and width, but the other is some fifteen fathoms in vertical 
extent and about five feet wide. From this contact one bears 
about 35° 8. of E.—N. of W., the other perhaps 25° 8. of E.— 
N. of W.; in their devious ranges, however, one preserves a 
certain parallelism with,—and occasionally touches and enriches, 
—a (lrawn) cross-vein; whilst the other takes the course of,—and 
now and then grazes—a lode, which is sometimes productive, not- 
withstanding its approximation to the strike of neighbouring cross- 
veins. In different parts of the considerable distances throughout 
which both have been explored, they vary from a few inches to at 
least sixty feet, as well in width as in height; thus lacking that 
great vertical range which is so essential a character of all Jodes, 
and resembling rather the pipe-veins§ of Carboniferous districts, 
in that they are bounded above, below, and on both sides, by 
barren (Country) rocks. Both decline towards the S. Dy § the one 
about ten, the other nearly eight, degrees. Their principal earthy 
constituents are quartz, schorl, and felspar ; their matrix, how- 
* Fox, Reports of the Royal Corn: Pol: Society, iv., p. 93. Henwood, 
Cornwall Geol: Trans: v., pp. 25, 225. 
+ Carne, Jbid, iii., p. 81. Dela Beche, Report, p. 336. Henwood, 
Cornwall Geol: Trans: v., p. 225. Thomas, (C.), Geology of Cornwall and 
Devon, p. 20. Von Cotta, Ore-Deposits, p. 419. 
+ Henwood, Cornwall Geol: Trans: v., pp. 21-24, Table xvi., Pl. ii., 
Fig. 4,5; Ibid, vii., pp. 179-184, Table i., Pl. viii., Fig. 1, 2,3. Salmon, 
Mining and Smelting Magazine, iii., pp. 139-148, Fig. 11, 12, 13, 14. 
§ Forster, Section of the Strata from Newcastle to Cross Fell, pp. 246 
to 249, 256. Wuuitney, Metallic Wealth of the United States, pp. 413-414. 
