In the autumn of 1871 I found in a large cavity or “vugh” in the schorlaceous granite of Boscaswell Downs, in the parish of St. Just, Cornwall, a number of black and opaque hexagonal prisms, having ragged terminations, which I at first took to be pseudomorpbs of black tourmaline (schorl), after quartz. They were set aside for further examination and forgotten until the beginning of the present year, when I undertook their examination.

I found that, although they were very compact, the sp. gr. was only 2.747, which at once negatived the idea of schorl, the sp. gr. of which ranges from 3.0 to 3.3. I then cut a number of sections for microscopic examination, and these at once shewed that the prisms were composed of clear and eolourless quartz, containing an immense number of tourmaline crystals, mostly very thin and arranged in feathery groups as in Plate III, figs. 1 to 4.