SANDSTONE OF THE AVESTERN COAST. 93 



the probable cause of the present detached state of 

 the several masses. That opinion is strongly confirmed 

 by taking an extended view of the west side of Sutherland 

 and Ross-shire. It will thus appear, that the country 

 consists of a basis of gneiss forming an irregular and 

 hilly surface, which in extreme cases varies in eleva- 

 tion from 100 to 1500 feet, but which often presents 

 a table land of considerable height with inequalities of 

 comparatively small account. On this base are placed 

 various mountains, either far detached from each other 

 or collected in groups ; and all rising to an average 

 altitude of about 3000 feet above the level of the sea, 

 or of 2000 above that of the gneiss. The stratification 

 of these, it has been shown, is either horizontal or slightly 

 inclined, with a variety of dip, in which the eastern 

 however prevails ; while the declivities of the mountains 

 on all sides, consist of the broken ends of the strata. 

 In no case does the declivity consist of the surface of 

 a stratum, as in mountains of micaceous schist or gneiss ; 

 in which it is usual to find the opposed declivities formed 

 alternately of the surfaces and of the edges of the beds. 

 It is scarcely necessary to say that mountains so formed 

 could not have been produced by the elevation of the 

 strata, as in the last named rocks ; and it is, on the 

 contrary, evident that, like mountains of trap, they owe 

 their present shapes to the abrasion of their sides.* It fol- 

 lows therefore, that the whole of this country has been once 

 covered with a body of sandstone, equal in thickness, 

 in certain points at least, to the present remaining 

 portions ; the variations of the dip marking the un- 

 dulations of that mass when in its entire state. The 

 extreme depth of this deposit, as far as it can now 

 be discovered, may be measured by Kea cloch, of 

 which the altitude has already been given; since the 

 strata are there nearly horizontal, and extend from the 

 summit to the base, where their further depth is con- 



* Plate XXX!. iiir.,4. 



