Mineralogy of Sky, 93 



beauty, which, although they seem to resist the injuries of time 

 far longer than the accompanying substances, at length also be- 

 come 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 pre- 

 sent 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 as- 

 sumes 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 circum- 

 stances 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 ac- 

 companied 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. Giesecke 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 

 Tock which I have already described, and that there is a corres- 

 pondence in the repositories of this substance in both countries. 



