Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/99

 two latter having frequently a greenish hue. Besides the decided. nodules of prehnite contained in it, the same mineral is intermixed throughout the rock, forming an integral part of it, and often passing into mesotype, as it appears to do in other more decided instances. It has been said by Haüy that prehnite has not been found forming an integrand part of rocks; but as a compound of a similar nature occurs in the Kilpatrick hills near Glasgow, an exception must be made in favour of these instances. I may here add, that a corresponding rock may be seen on the opposite coast of Raasa.

It is perhaps superfluous to say that nodules of chalcedony, often hollow and containing crystallized quartz, are occasionally found in the trap rocks of Sky, since they are of such common occurrence in this substance. The cavities are sometimes, in addition, sprinkled with crystals of stilbite, of analcime, and of chabasite.

Of those mineral substances which are the least frequent in trap rocks, steatite occurs in considerable quantity; it is tender, and always of a greenish dirty hue. It is sometimes found in very small nodules; but in other places, as near Dunvegan and in the parish of Kilmuir, it is so abundant that it has been dug up with the intention of exporting it for economical purposes.

I have already mentioned that epidote is found both in the clinkstone and in the trap, but in too small quantities to render any further account of it necessary. It is thus far worthy of notice, as it is one of the few minerals which seems to appertain to rocks of very different characters and periods of formation.

The carbonate of lime to which I alluded when speaking of the chabasite, is found in company with this mineral and with the analcime, occupying along with them cavities in the trap: it presents but one form, that rhomb which is called the inverse, and