various parts of Scotland, 415 



4. Of an uniform dove colour, very compact and translucent, 

 assuming an excellent polish. 



5. Pure w^hite/of a large platy fracture, and translucent appear- 

 ance, capable of being used in plain ornaments, but too transparent 

 for sculpture. 



6. White, with irregular yellow stains, from serpentine inter- 

 mixed ; extremely fine, compact, and fine grained splintery. 



7. Intersected by thin laminae of schiefer spar, of an exceed- 

 ingly splendent appearance. 



Isla. 



My object in laying before the Society the series of specimens 

 collected in Isla, is the correction of some mistakes which have been 

 entertained about the nature of its limestone district ; a district of 

 some importance in more than a speculative view, as it forms a 

 mining field In which lead ores have been wrought to a consider- 

 able extent. My researches in Isla having been limited to this 

 particular part of it, I shall confine myself to that which I 

 have seen, referring to Mr. Jameson's book for such further Infor- 

 mation as may be found in it. I may, however, venture to point 

 out this island as a spot In which the very important circumstance 

 alluded to In another place, of the connection of the quartz rock 

 with the mica slate, and clay slate, might be studied to great ad- 

 vantage. This deduction Is not drawn from my own observations, 

 which were not sufficiently numerous to enable me to decide on a 

 question so important, but from the narrative of Mr. Jameson, 

 who appears to describe frequent alternations of those different 

 classes of rocks. Extensive and correct observations on Isla, would 

 probably determine the true relative sera of the quartz rock, and 



