Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/121

 partly through granite, partly through schist. A further search enabled me to obtain several beautiful specimens containing many varieties in the form of the crystal as well as in colour. The crystals are for the most part well-defined, but the largest scarcely exceed half a line in length or breadth, and some of them are accompanied by black pecherz (Uran oxydulé Haüy); they were found on, or in the cavities of, considerable blocks of a hard substance enclosing portions of decomposed felspar; but quartz formed the principal part of the mass, which had decidedly the character of being an aggregation resulting from the decomposition of granite. The specimens in my possession, are for the most part thinly coated with a black substance which I consider to be the pecherz in a pulverulent form; internally they are of a redish hue, arising probably from iron, with which the mine abounds, and occasionally some minute rounded portions of iron hæmatites may be observed. The depth at which these blocks were found, according to the best information I could obtain, was about 90 fathoms from the surface, in a copper vein.

I also obtained many specimens containing beautiful and well defined crystals of the oxyd of uranium from Tol Carn mine, which is about two miles north of Carharack, and near St. Die. The veins of Tol Carn mine pass through a decomposed granite, of which the prevailing substance seems to be felspar, enclosing portions of quartz and silvery mica. With this substance the vein seems to have been filled in that part in which the oxyd of uranium was found, but it was of a dark colour, and had attained, though considerably friable, a texture much more firm than that of the neighbouring country; and as, on almost every specimen, the crystals of the oxyd of uranium were accompanied by pecherz,