The crystals represented by figs. 66, 68, 69, 70, 71, 79, are about the size of a common quill, and were presented to me by a gentleman of Penzance, who knew not whence they were brought; judging, however, from a superb specimen in my collection, on which there are some of the above varieties in form, and of about the same size, and which is from Gavrigan stream works in St. Mewan, I presume them to be from the same place.
The crystals delineated by figs. 72, 73, and 86, are singularly beautiful, and present, though scarcely a line in length, both terminations complete. They were all taken from the same specimen, which is the only one of the kind that I have seen, but from what mine it was brought I am unable to say, it having accidentally been left in London by the captain of a Cornish trading vessel. The crystals represented by fig. 67. were found detached in a vein near the Land's End. Of the singular variety, fig. 98. I have four crystals, their form is occasioned by the elongation of one plane of the second modification on one pyramid, and of the opposed face on the other; they are of a light brown colour, and translucent.
Eighth Modification.
This modification, like the preceding, consists in a decrease on each of the four solid angles, caused by the meeting of the two pyramids of the primitive form, by which each is replaced by four triangular planes, placed on the edges, but inclining more than those of the preceding modification on the axis passing through the solid angles, fig. 106. Pl. 20. By fig. 107. the planes are shewn in an advanced state.
The two figures which alone compose the series of this modi-
