34 Dr. Mac Culloch's Sketch of the 



rock of Jura ; yet there are evident marks of stratification, which 

 in many places are sufficiently regular and extensive to justify the 

 belief that it has once possessed a greater degree of regularity and 

 extent, which have been disturbed by subsequent changes. The 

 predominant colour is a bluish or greenish grey, and its most 

 general aspect that of a compact splintery quartz, often obscurely 

 granular, and every where traversed by veins of ordinary white 

 quartz. At Kyleaken it has a brown colour and a fat appearance, 

 but becomes white and harsh on exposure to the weather, in con- 

 sequence of the decomposition of the felspar which it contains. 

 The great thickness of the mass here, compared with the thinness 

 of the similar rock at Loch Eishort, is no proof of non-identity, 

 since in so many other cases we find strata differing, in perhaps as 

 great a degree, in thickness where we have the most satisfactory 

 evidence of their continuity. I have not observed this rock in any 

 other part of Sky, and it will presently appear that it could not be 

 expected any where but beneath the sandstone near Loch Scavig. 

 I shall not be surprised if it exists at the southern side of Soa under 

 the sandstone beds, since that is its place, but this part of that island 

 was unfortunately the only one which I could not reach. That it 

 is a bed of great extent in this country, although so little visible, is 

 confirmed by its being found in Rum, and in the same position, as 

 I have ascertained. 



The rock next in order to this is the red sandstone, and the 

 connection between the two is equally distinct at Loch Eishort, 

 where they are found following each other In a regular order and in 

 intimate contact, there being indeed a gradual passage from the 

 blue quartz rock into the red sandstone by a- series of intermediate 

 changes both in point of hardness and colour. The same transition 

 will be found near Kyleaken on the eastern side, although I cannot 



