Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/417

Rh improbable but that plasma as well as heliotrope may be an inmate of the trap rocks of Scuir-more.

A substance is occasionally brought from India, known to lapidaries by the name of brown carnelian, and it is esteemed peculiarly rare. This substance also is found among the chalcedonies of Rum, occupying the same situation as the green varieties, and differing from them only in colour. It probably owes its stain to iron. Motley mixtures of brown, and green, of considerable beauty, add to the variety of ornamental stones which these rocks contain.

The apparently inaccessible nature of the southern shore of Rum, prevented me from extending further my observations on this interesting island. But in coasting it slowly along, it offered the same general appearance as the cliffs I have now been describing which look toward the island of Canna, exhibiting one formidable wall of basaltic aspect, reposing on a base of sandstone. It will be for more successful geologists to examine whether circumstances equally interesting, and of a different nature, may not be found among the caverns and ruins of this repulsive, if not absolutely inaccessible coast.

I have little to add to the description of Egg given in the “Mineralogy of the Scottish isles,” but the following fact relating to the situation of the promontory called the Scuir of Egg, which is not noticed in that work. The columns which form this most magnificent precipice, exceeding in grandeur and picturesque effect even the far famed Staffa, are of a black pitchstone porphyry. They are disposed in various perpendicular, inclined, and horizontal directions, and are either straight, or curved, but never jointed. The felspar which they contain is the glassy variety. The lines