Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/376

 specimen of it that exhibits an interesting fact. Its surface shews the union of an immense number of small rectangular prisms, all, or nearly all, having their planes in a parallel direction; but a very great number of them are very distinct in all the extent of their square surface. This texture appears to have been occasioned by a very slight alteration. The matrix of this bardiglione is an indeterminate massive quartz, to which there adheres a fragment of foliated micaceous rock, mingled with galena and some iron pyrites. It came from the lead-mine of Pesai, near Mont Blanc.

4. With small laminæ intersecting each other in different directiions. The bardiglione of Vulpino frequently presents us with this variety, which sometimes has a very deep bluish colour, and is frequently mixed with a few particles of quartz. We are indebted to M. Fleuriau de Bellevue for a knowledge of the different varieties of the bardiglione at Vulpino. It was he who found that this substance, which takes a very fine polish, and is employed by the statuaries of Bergamo and Milan for making slabs, chimney-pieces, &c. differed essentially both from carbonate of lime and gypsum. The first analysis of this substance having shewn it to contain sulphate of lime and quartz, the latter in the proportion of 0.8, it was called quartziferous sulphate of lime; till a second analysis by Vauquelin ascertained its real nature. The interposition of quartz, and the interruption of contiguity occasioned by this interposition, diminishes its specific gravity, which was found to be 28.78 by the Abbé Haüy, who some time after discovered that it belonged to the bardiglione. The quartz interposed in this substance may sometimes be perceived by a good lens.

Sometimes too this variety of bardiglione, and more particularly the following, in the granular state, includes particles of carbonate of lime, but always in very small quantity.