former existence of Glaciers in Forfar&hirc. 581 



proceeds to illustrate his subject by describing in detail the phe- 

 nomena presented by the valley of the South Esk and those of its 

 tributaries. 



The South Esk springs from a shallow lake nearly 3000 feet 

 above the level of the sea, and twenty miles from Strathmore. For 

 six miles the river flows through a district composed partly of gneiss, 

 traversed by veins of granite or eurite, and partly of granite. The 

 fragments derived from this high region may be traced downwards 

 continuously for twelve miles to Cortachie ; and as a proof that the 

 detritus forming the lateral mounds has followed the same down- 

 ward course, INIr. Lyell states that it preserves throughout, as well 

 in the main as in the lateral glens, an uniformly grey colour ; while 

 the detritus of the lower zone of mica-slate is invariably tinged red, 

 this colour being also imparted to the debris of the still lower por- 

 tions of the glens, notwithstanding the intermixture of pale brown 

 materials obtained from the clay-slate of that district. Another 

 proof of the detritus not having been drifted upwards, is the absence 

 in the higher portions of the glens of the blocks of pure white quartz 

 which abound in the region of mica-schist, and have been derived from 

 the numerous veins and beds of quartz belonging to that formation. 

 The chief exception to this arrangement is a boulder of conglomerate 

 in the bed of the Proson, evidently derived from hills two miles to 

 the south, but which are considerably above the level of the glen. A 

 few other similar exceptions have been noticed, but the distances to 

 which the stragglers have been traced are inconsiderable. The phse- 

 nomena exhibited by the lateral mounds, Mr. Lyell states, agree 

 well with the hypothesis of their being the lateral moraines of gla- 

 ciers ; and he adds, that he had never been able to reconcile these 

 phsenomena, particularly the want of stratification, with the theory 

 of the accumulations of the detritus during submergence, and the re- 

 moval by denudation of the central portions of a deposit which had 

 by that means filled the glens. The distribution of an enormous 

 mass of boulders on the southern side of Loch Brandy, and clearly 

 derived from the i^recipices which overhang the Loch on the three 

 other sides, is advanced as another proof in favour of the glacial 

 theory. It is impossible to conjecture, Mr. Lyell says, how these 

 blocks could have been transported half a mile over a deep lake ; but 

 let it be imagined that the Loch was once occupied by a glacier, and 

 the difficulty is removed. Loch Whorral, about a mile to the east 

 of Loch Brandy, is also surrounded on its north, east and western 

 sides by precipices of gneiss, and presents on its southern an immense 

 accumulation of boulders with other detritus, strewed over with 

 angular blocks of gneiss, in some instances twenty feet in diameter. 

 This moraine is several hundred yards wide, and exceeds twenty 

 feet in depth, terminating at the borders of the plain of C'lova in a 

 multitude of liillocks and ridges much resembling in shape some 

 terminal moraines examined by Mr. Lyell in Switzerland. 



'i'hc great transverse barrier at Glcnairn, where the valley of the 

 South Esk contracts from a mile to half a mile in breadth, and is 

 flanked by steep mountains, Mr. Lyell formerly regarded as very 



