SKY. MINERALS. 419 



6. White marble variously mottled and veined with 

 grey, yellow, purple, light green, dark green, and black. 



The ornamental coloured varieties here described, 

 scarcely yield in beauty to tne analogous specimens of 

 ancient marbles, and like many of those in Scotland, they 

 will be found to owe their green and yellow colours to 

 serpentine. This is also the case in Glen Tilt, at Bala- 

 hulish, and in Tona. But the most obviously valuable 

 variety is the white, which seems to possess most of the 

 qualities requisite for the purposes of statuary. As I 

 have however entered somewhat at large into the eco- 

 nomical value and uses of this marble in the paper 

 formerly published in the Geological Transactions, I need 

 here take no further notice of it. 



I may terminate this account of the minerals of Sky 

 by mentioning that beds of marie are not unusual in the 

 island. As they are always found in the vicinity of the 

 limestone strata, there can be little doubt respecting their 

 origin, although it is difficult to conjecture the nature of 

 the process by which the calcareous beds undergo this 

 decomposition. 



It ought also to be added to this catalogue of minerals, 

 that oxidulous iron is found in thin veins traversing the 

 hypersthene rock, and with that remark I shall now close 

 the account of this very interesting island.* 



* While this sheet was printing, the arrival of some specimens illegally 

 detained at the Custom-house of Leith, compels me to add as a note, an 

 interesting fact respecting the hypersthene rock which should have 

 appeared in the text at page 390. It is not the only blemish due to the 

 same cause. This is the presence of garnets in that rock, in the hill 

 Scuir na Streigh. They are abundant, giving to the specimens a particu- 

 larly granitic aspect, and like the graphic variety formerly described, 

 adding another strong resemblance to that already existing between 

 granite and hypersthene roek. 



