498 RUM. MINERALS. 



Arsteval or Traleval. I also found pieces of a reddish 

 felspar porphyry on Oreval, of which the place was pro- 

 bably not far off, since they were near the summit. 



On the beach under Scuir more, fragments of two kinds 

 of pitchstone occurred, the one of a black, the other of an 

 olive green colour ; but whether from the sandstone or 

 the basalt it is impossible to determine, since these are 

 both far out of reach. There is nothing in the mine- 

 ral character of either which demands a detailed de- 

 scription. 



It is only among the fragments on the same beach that 

 the heliotrope can be procured, large quantities of it 

 falling together with portions of the rock in which it is 

 imbedded. This beautiful mineral is not peculiar to this 

 part of Scotland, since I have found it in the hill of 

 Kinnoul, in Kerrera, in Mull, and in Ayrshire. But it 

 offers here a considerable number of varieties, the prin- 

 cipal of which it will be useful to describe, because they 

 point out so clearly the origin and composition of this 

 mineral, which I have formerly shown * to be a compound 

 of green earth and chalcedony. The chalcedonic basis 

 itself varies in aspect and composition, and thus proves 

 a fundamental cause of variety in the appearance of the 

 heliotrope ; being at times of the most usual character, 

 while in other cases it tends on the one hand to quartz, 

 and on the other to chert. Hence the fracture of the 

 heliotrope is sometimes sharp and conchoidal, with the 

 lustre of resin, while at others it is earthy, or resembles 

 wax. The series of colour which is here found among 

 the specimens, renders it easy to trace the progress of 

 this mineral from common white chalcedony, or from 

 chert, to the deepest green heliotrope ; according to the 

 proportions of green earth which it may contain. At first 

 the basis is slightly tinged, either partially or generally, 

 with green. This by degrees increases, passing through 



* Geological Transactions, vol. ii. 



