1824.] the Rocks of Mount Sorrel, fyc. 19 



afforded, by several trials, an angle so very near to one belong- 

 ing to cleavelandite, and which of course does not belong to 

 felspar, that we have scarcely a doubt of the existence of the 

 former mineral in this rock also ; the green crystals are some- 

 times obviously included in those of a red colour : and we con- 

 ceive it to be not improbable, that the close intermixture of these 

 two minerals in that which is termed compact felspar, will 

 account for the presence of soda and potash, both of which, it is 

 observed by Dr. Mac Culloch, are constant ingredients of that 

 substance. Both the red and green varieties yield to pressure 

 with a hard mineralogical knife, the green being somewhat the 

 softer of the two, and therefore appear to be less hard than 

 felspar usually is : sometimes this rock contains minute, slender, 

 and transparent crystals, which, from their superior hardness, 

 we consider to be felspar, and specks of green or of yellowish 

 steatite, and oxidulous iron in minute regular octohedrons ; 

 quartz is a frequent ingredient ; mica and epidote occur more 

 rarely ; in the quarry W of Grooby, we observed the rock 

 traversed by veins, in one instance two inches thick, of a hard 

 flesh-coloured substance, which may be cleaved into curvilinear 

 rhomboids, in the cavities of which were minute crystals in that 

 form ; and as these crystals, and the substance including them, 

 effervesce slightly, and dissolve slowly in diluted muriatic acid, 

 and as the crystals afforded angles of about 106° 30' by the 

 reflective goniometer, we conclude them to be magnesian car- 

 bonate of lime. The sides of the veins are coated with chlorite, 

 which also is included in the vein itself. 



In the quarry on the E of Grooby, we perceived a vein of 

 quartz and chlorite, and some appearance of the rock being 

 traversed by a dyke in a N and S direction, but io too rude a 

 manner for us to ascertain the fact, the walls, or what we con- 

 ceived to be such, being very irregular and indeterminate, and 

 the substance of the supposed dyke being composed of the same 

 materials as the rock inclosing it, but much finer grained. 



Although the connexion of these rocks with those of Cham- 

 wood Forest was not perceived, we consider it to be worthy of 

 note, that after descending the south-western slope of Beacon 

 Hill, and traversing a field at its base, we found, beside a small 

 brook, some rocks of very considerable dimension, aud which 

 we fully believed to be in situ, so perfectly resembling those of 

 Grooby, that it was impossible to doubt their identity of compo- 

 sition ; and it may be remarked that fragments of the same rock 

 almost constitute the walls of the neighbouring fields. Whether 

 this rock be a dyke, or in what manner it is connected with the 

 forest rocks of the surrounding elevations, we had no means of 

 ascertaining, since it is the only one which overtops the herbage 

 in this comparatively low situation. 



c'J 



