

NORTH RONA. GEOLOGY. 211 



or perfectly transparent and colourless. Besides these, 

 there occur large concretions of opalescent quartz, varying 

 from a highly diluted to a more perfect milkiness, and 

 occasionally tinged with blue, in which case the specimens 

 possess considerable beauty. In other veins there are 

 found concretions of felspar equally large and beautiful, 

 of a French grey colour, accompanied by quartz of a 

 similar tint, and, like the former, these are occasionally 

 mixed in a graphic manner. 



It is not improbable that a more rigid search might 

 add something, to the varieties at least, of these sub- 

 stances ; but the rising of the wind and sea rendered 

 a precipitate retreat necessary. The addition of a few 

 specimens to the catalogue would have been dearly 

 purchased by even a week's residence in the stormy and 

 solitary abode of North Rona, 



