Geography of Scotland, Sutherland, &c. 285 



facts connected with the greater physical features of 

 Scotland, omitting minor details. 



In the extreme north of Scotland, in Sutherland 

 and Caithness, the manner in which the strata gene- 

 rally lie is shown in the following diagram. (See Map, 

 line 4.) 



FIG. 54. 



I have already mentioned that, in some of the 

 Western Isles, from the Lewes to Bara, and in the north- 

 west of the mainland of Scotland, from Cape Wrath to 

 Gairloch, the country, to a great extent, consists of 

 certain low tracts formed of Laurentian gneiss (No. 1 ), 

 twisted and contorted in a remarkable manner. Upon 

 this old gneiss the Cambrian rocks (2) lie, rising often 

 into mountains, which face the west in bold escarp- 

 ments, and slope more gently towards the east. These 

 strata frequently lie at low angles very unconformably 

 upon the old Laurentian gneissic rocks ; the meaning 

 of this being, that the latter were disturbed, contorted, 

 and extremely denuded, before the deposition of what I 

 believe to be the fresh-water, the Cambrian strata that 

 lie upon them. The bottom beds of the latter consist 

 of conglomerates of rounded pebbles, partly derived 

 from the waste of the Laurentian gneiss, which, there- 

 fore, is so old, that it had been metamorphosed and 

 was land before the deposition of the Cambrian beds. 

 Upon these unaltered Cambrian rocks, and again quite 

 unconformably, the fossiliferous Lower Silurian strata 

 (3) lie, sometimes in the manner shown in the diagram ; 

 and conclusions, regarding upheaval and denudation, 

 may be drawn from this second unconformity, similar 



