Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/373

 which I mentioned at the time in the brief account I gave of this substance in the Journal des Mines, No. 77, is very singular, when we consider the local circumstances of the bardiglione in which it occurred.

There is another variety of this substance in determinate crystals, often of considerable bulk, and imbedded in a mass of compact bardiglione of a reddish-brown colour, penetrated with gypsum and sea-salt. In this mass different cavities are perceivable, in which the gypsum, likewise coloured red, is in small crystals; and some of these also include sea-salt, perfectly pure, and of a red colour. The crystals of bardiglione which are scattered through this mass, while they remain adhering to it, appear themselves reddish, on account of their transparency; but, when they are detached, their colour is a deep grey. This variety comes from the salt-works of Bex, and is that which I have already mentioned as having its colour destroyed by heat.

Bardiglione of indeterminate Crystallization.

1. Approaching to a determinate. Among the crystals of this substance there are several in very thin rectangular laminæ, which grow thinner by imperceptible degrees towards the two narrow sides of the prism, and this thinning, which varies considerably, is subject to no law.

At other times, as the edges of the primitive tetrahedral prism, according to the observations hitherto made, may be subjected to six different retrogradations with regard to the placing of the crystalline laminæ, the crystals having undergone these six retrogradations in succession, without the crystallization having perceptibly rested at any of them, the faces have assumed a curvilinear figure throughout