14 MONOGRAPH OF DURA DEN. 



when the quartz and felspar are scarcely visible from their 

 extreme attenuation, it merges into a variety of Hornstone. 



Gneiss, the lowest of the stratified rocks, is likewise the 

 most widely diffused of the Scottish primary series, filling an 

 area of 9600 square miles, and with scarcely a break over this 

 extensive district of country. It occupies nearly the entire 

 northern counties of Sutherland, Ross, and Inverness ; great 

 part of Nairn, Elgin, Aberdeen, and Perth shires ; most of the 

 western islands, as Tiree, Coll, South and North Uist, Harris, 

 and Lewis, consist of the formation, as also considerable tracts 

 in Orkney and Shetland. While in a soft state, or from the 

 vast pressure to whicli it has been subjected, this rock often 

 assumes the most singular contorted appearances, whole miles 

 presenting twistings and undulations as if the substance had 

 been moved and tossed like a stormy sea, and sometimes 

 crumpled and bent, or rolled into gentle unbroken flexures like 

 a web of cloth. It will thus, in such cases, exhibit beautiful 

 and picturesque aspects ; and where exposed in ravines along 

 with other rocks, with which it finely contrasts, no better 

 pictures or groupings of rock scenery are to be met with. 

 But in general, where the gneiss is unbroken, and as it seldom 

 rises into peaks or serrated ridges, the districts in which it 

 prevails are rather monotonous and un pleasing, not unfrequently 

 disfigured by spongy heaths and boggy wastes. The most 

 desolate, uninteresting portion of the Highlands is unquestion- 

 ably the north-western districts of Ross and Sutherland, where 

 the hills of this formation are all flat and shapeless, sur- 

 rounded by unvarying solitudes of brown moor, interminable 

 deserts of sand, and scarcely enlivened by a river, or broken 

 in their silence by a waterfall. Gneiss is the oldest rock 

 known in the records of Geology — the lowest floor of the most 

 ancient seas — ^probably the first dry land that rose above their 

 surface ; and here, in these sterile wastes, presenting a scene 

 of almost primitive chaos and desolation. 



The next number of the series, in the ascending order, is 



