514 Geological Society. 



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 

 phaenomena, 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 precipices 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. liyell 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 l3orders of the plain of Clova in a 

 multitude of hillocks and ridges much resembling in shape some 

 terminal moraines examined by Mr. Lyell in Switzerland. 



The great transverse barrier at Glenaim, 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 

 difficult of explanation. Seen from below, this barrier resembles an 

 artificial dam 200 feet high, with numerous hillocks on its summit. 

 On the eastern side it appears to have been denuded to the extent 

 of about 300 yards by the Esk. Its breadth from north to south 

 is about half a mile. The lower part, 30 feet in depth, laid open 

 in the river cliff, consists of impervious, unstratified mud, full of 

 boulders ; but the total vertical thickness of this deposit is stated to 

 be from 50 to 80 feet; and the upper part of the barrier is com- 

 posed of from 50 to 100 feet of very fine stratified materials. It is 

 not possible, Mr. Lyell observes, to account for the accumulation of 

 this barrier by the agency of water, particularly as no tributary 

 joins the Esk at this point ; but if j;he barrier be supposed to be the 

 large terminal moraine of a receding glacier, then its form and 

 position, he says, are easily to be understood. M. Agassiz, in his 

 work on glaciers, shows, that when these masses of ice enter a nar- 



