Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/144

134 west or metalliferous veins in the direction nearly of north and south, are technically termed Cross Courses. They rarely produce copper or tin, or any other metallic substance. They vary from half an inch to a few feet in width: the underlie of some is east, of others west; others again have little or no perceptible underlie, but are nearly perpendicular to the horizon. In some tracts of the mining country they are of very frequent occurrence, as the accompanying ground plan of Herland mine will evince.

Cross Courses, or north and south veins, may be subdivided into 1st. a Quartzose vein, to which the general term of Cross Course has been given—2nd. a vein containing a soft marly or clayey substance of a bluish or whitish appearance, called a Flucan; and 3d, a vein containing a substance of an ochreous and friable nature and of a yellow colour, called by the miner a Cross Gossan. Every cross course or cross gossan is however accompanied by a flucan. In speaking of these veins the miner sometimes gives them their technical appellations, but he is more habitually disposed, whatever the substances of these veins may be, to call them by the familiar term of cross courses.

The principal advantage derived from the north and south veins is that, when their substance is flucan, or even when a continuous vein of flucan, however thin, accompanies the quartz or gossan, they prevent the water of the neighbouring country from troubling a mine, and they are sometimes left to perform that useful office, as was the case between Huel Sparnon and East Huel Sparnon, near Redruth. But their disadvantages are numerous; for although the regular metalliferous veins are occasionally found to be but little or not at all disturbed by the passing of the substance of the cross vein through them, except by the mere division of the load, it more often happens