Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/378



This variety is less compact in its texture than compact carbonate of lime, or compact feldspar: its substance, at least in all the specimens which I have hitherto had an opportunity of observing, being more or less mixed with small particles of lamellar bardiglione. Hence its fracture is very rough and irregular; but we can always distinguish in it those little prominent and somewhat detached splinters, which are characteristic of minerals having a compact structure. This variety has generally a slight semi transparency at its edges.

1. Mixed with quartz. This variety of the compact bardiglione occurs with the lamellar variety at Vulpino; the quartz which it contains is sometimes visible with a good lens.

2. Mixed with sea-salt. The salt-rock of Arbonne belongs to this variety. Hitherto this rock has been considered as a gypsum mixed with sea—salt; but all the specimens I have yet seen, and which have been sent to me by my friend Gillet de Laumont, belong no doubt to the species bardiglione. This variety includes also in its substance very brilliant small laminæ of bardiglione, and its fracture is more irregular than that of the pure compact variety.

The salt-rock of Arbonne presents two varieties of this substance; one of a dirty grey, and the other a little reddish. The latter of these varieties is somewhat closer and finer grained than the other, and it is also less loaded with sea-salt. Very small dodecahedral crystals with pentagonal faces of iron pyrites, are disseminated through its substance. Small globules of compact bardiglione, very easily separable from the substance in closing them, are likewise included in it. These little globules are destitute of the brilliant laminæ observable in the surrounding mass, are of a brown colour,