Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/162

152 It was in this mine, as has been already noticed, that silver was discovered in Convocation Cross Course, as well as a very small quantity in Rusty Cross Course.

of porphyry also occurred in this mine; their effect on the N. and S. and E. and W. veins was similar to that produced by a channel of the same description in Pleasure, Fancy, and North Herland mine; their underlie and thickness are also about the same.

The underlie of the Slide is in the same direction as that of the channel of porphyry, but not so quick. Its substance was flucan of three or four inches in thickness; it passed through the cross courses and flucans. It also traversed the metalliferous vein, the course of which it interrupted, and heaved about fifteen inches, but whether to the north or south I know not. The load of the metalliferous vein was found to be richest a fathom or two along the run of the slide, both above and beneath it.

Tin Croft mine has been worked many years; and has yielded large profit both to the lord of the soil and to the adventurers. It was first worked for tin, principally, I believe, if not wholly, on the two most northerly veins. The country in which the mine is situate is for the most part schistose, but some remarkable alternations of schist and granite were discovered while working the two veins on the south, the probable cause of which appears to be this, that as these veins run parallel with and at the foot of the hill called Carn-brae, which is wholly of granite, the irregularities in the granite were supplied by a deposition of the schist. In no other part of the mine does granite appear, except that in following down two of the veins, as is noted on the accompanying section, they were