Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/101

 beauty, which, although they seem to resist the injuries of time far longer than the accompanying substances, at length also become rotten, and fall into an ochry powder. Distinct concretions are to be found exhibiting the primitive form, and which appear to be true crystals, since they are detached from the surrounding substances. More generally however, it is without form, while in many cases it is intermixed with the dark felspar so as to present the graphic character, the crystals of felspar being defined, and the hypersthene occupying the interstices. The lustre of this mineral is always highly metallic, but the specific gravity of the specimens which I examined did not exceed 3.342. The colour is various; in general it is of a purplish black, sometimes steel grey, and more rarely of a pale whitish grey, while it often assumes the hue, together with the lustre of polished brass, when it has long been exposed to the air.

Hypersthene has been found in Aberdeenshire, but the circumstances which accompany it have not been described, nor the nature of its connections ascertained. As far as can be determined by this instance, it must be considered as an inmate of the trap family. Having also found it in the island of Rum associated with the same class of rocks, additional confirmation is afforded of this connexion. That of Labrador is known, like the present, to be accompanied by dark felspar; but the rock which is the common repository of both has not been described by the missionaries, to whom we are indebted for the only knowledge we possess of that country. Mr. Giesecké considers the Labrador felspar of Greenland as belonging to what he calls the “ Syenite formation,” and it is not improbable that his syenite formation resembles the rock which I have already described, and that there is a correspondence in the repositories of this substance in both countries.