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transported debris, with a nearly flat top, and sometimes with two 
steep sides, one towards the river, and the other of less height to- 
wards the mountain; and 8rdly, the stratified gravels, sands and 
clays which overlie the unstratified detritus. Mr. Lyell confines 
his observations principally to the second and third divisions. 
The terraces or lateral mounds very generally increase in width 
and depth as they descend from the higher to the lower glens, attain- 
ing in the latter sometimes a thickness of 100 feet, and occa- 
sionally so great a breadth as to leave only sufficient room for the 
river to pass. The inferior part is always unstratified, consisting of 
mud and sand, in which large angular and rounded fragments of 
rocks are imbedded. ‘hese boulders are more and more rounded 
as their distance increases from the hills whence they could have 
been detached; but they are more frequently flat-sided than pebbles 
which have been rounded by water; and they become more diversi- 
fied in character by the junction of every tributary glen. In the 
upper part the mounds often consist of 40 to 80 feet of the same 
materials as the lower, but regularly stratified. Mr. Lyell then 
proceeds to illustrate his subject by describing in detail the phz- 
nomena presented by the valley of the South Esk and those of its 
tributaries. 
The South Esk springs fort 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, Mr. 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 
whichabound 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 phe- 
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 
phenomena, 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 
