Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/123

 and one specimen of wavellite from Stenna Gwyn near St. Austin on which some crystals of a light yellow colour are deposited.

But by far the most brilliant specimens of the oxyd of uranium that have been found in this, or perhaps in any other country, were discovered within the last three or four years in Gunnis Lake copper mine near Callington in Cornwall. The gangue of two specimens in my possession is of quartz, bearing the characteristic marks of being the result of decomposed granite, and which is rather confirmed by the circumstance of its cavities being filled with grouan, or decomposed felspar, of a flesh colour; of another specimen, the gangue is wholly a hard gossan. All the crystals from this mine that I have seen are described by fig. 15; they are extremely thin, but on some specimens they are more than half an inch in diameter. They are for the most part lying flat together, forming fasciculi which interrupt each other at various angles, and give an extremely beautiful appearance to the group. In Gunnis Lake mine the oxyd of uranium was found at about 90 fathoms from the surface, and in a part of the vein in which gossan abounded. On the few specimens in my possession from that mine, I have not noticed any trace of pecherz, but on those from Tol Carn and Tin Croft mines, particularly the former, it prevails very much. It is sometimes of a resinous transparency, but is more generally of a dark brown or black, either amorphous or in globules: on several specimens from Tol Cam mine it is quite friable.

It has already been said that the crystals of this substance from Tol Cara and Tin Croft mines, from which the drawings of the accompanying series were made, are for the most part very small; all the larger ones are so deeply striated in a horizontal direction, as