200 Mr Lyell on the former Existence of 



ing only space for the river to pass. The South Esk springs from a shal- 

 low lake, twenty miles from Strathmore, and nearly 3000 feet above 

 the level of the sea. For the first six miles, the river flows through a re- 

 gion of granite or gneiss, and the fragments of rocks derived from it may 

 be traced to Cortachie, a distance of twelve miles ; the detritus also in 

 this glen, and in all the others composed of granite and gneiss, preserves 

 throughout a uniform grey colour. On entering, however, the zone of 

 mica-slate, it is invariably tinged red in every glen, and this colour is 

 imparted to the detritus in the lower portions of the glen, notwithstand- 

 ing the intermixture of the pale brown materials obtained from the clay- 

 slate district. Another proof of the downward course of the transported 

 matter composing the mounds, is the rare occurrence of fragments of 

 quartz till the glens enter the mica schist region, where thick beds and 

 veins of pure white quartz abounds. This distribution of the detritus, 

 and its arrangement in mounds along the sides of the glens, Mr Lyell 

 says, agrees well with the hypothesis of glaciers and their lateral mo- 

 raines ; and is not reconcilable with the theory of submergence, and the 

 subsequent removal by denudation of the central portion of a deposit sup- 

 posed to have filled the bottom of the glens. The total want of stratifi- 

 cation he also urges as a proof that the materials were not deposited from 

 water. The glacier theory is farther shewn to offer the only explanations 

 of the phenomena presented by Loehs Brandy and Whoral, situate 1500 

 feet above the sea, and 600 above the Kirktown of Clova. Loch Brandy 

 is surrounded on three sides by lofty precipices of gneiss, while on the 

 south it is bounded only by an enormous accumulation of sand, mud, and 

 fragments of rocks, evidently derived from the cliffs which overhang the 

 lake on the east, north, and west. It is impossible, Mr Lyell observes, 

 to conceive how these great masses could have been conveyed over a deep 

 lake ; but if it be supposed that the cavity occupied now by water was 

 once filled with a body of ice, it is easy to account for the transport of 

 large boulders from the northern to the southern side of the cavity, and 

 their mode of distribution beyond it. Loch Whoral presents analogous 

 phenomena : and the immense mass of detritus which extends from its 

 southern side, terminates in the plain of Clova, in a multitude of hillocks 

 and ridges, resembling in shape some of the terminal moraines of Swit- 

 zerland. One of the features in the transported materials of the South 

 Esk, formerly regarded by Mr Lyell as very difficult of solution, is a great 

 barrier at Glenaiin, where the valley contracts to scarcely half a mile in 

 width, and is flanked by steep mountains. Viewed from below, the bar- 

 rier resembles an artificial dam, 200 feet high, and divided along its sum- 

 mit into hillocks. On the east side, it is cut through by the Esk, and its 

 breadth is about half a mile. Behind it, is a flat plain, four or five miles 

 long, and a mile and a half broad, through which the Esk meanders ; 

 and that it was once covered by a lake, is proved by some deep drains, 

 which exposed a succession of horizontal beds of sand, clay, and drift- 

 peat. The lower part of the barrier, thirty feet in depth, laid open in the 



