130 
THE GEOLOGIST. 
Ness and Locli Lochj, while these lakes have been disjoined from the 
sea by the large alluvial plains that now extend from them at each 
end, along the courses of the Lochy and the iSTess. The operations 
required in coDstructing the Caledonian Canal have ascertained the 
reality and extent of these alluvia, while daily observation shows 
that they are in many places at least receiving an augmentation, 
that has a tendency at some far distant period to obliterate the lakes 
and convert the whole into one prolonged strath, of which the future 
summit will be Loch Oich or some point in its vicinity. If, indeed, 
we examine the changes which the lakes of Scotland are now under- 
going, we shall find that they are receiving accumulations of alluvial 
matter at all the points where they are fed by the surrounding 
streams, while a comparatively small quantity of this alluvium is car- 
ried towards the sea. The result of this operation is to obliterate 
them and to convert them into alluvial valleys or straths. Instances 
of this revolution, more or less perfected, are numerous ; while no 
case of the obliteration of a lake by drainage, similar to that of Glen 
E-oy, can be pointed out." 
But it is at this point of his argument that Macculloch encounters 
the most serious objection to his theory ; not that that theory, as far 
as the ancient existence of a lake in the Glen Eoy region is con- 
cerned, is erroneous ; not that he was wrong in attributing to the 
action of the standing water of that lake, the erosion of the "parallel 
roads " of that and the neighbouring glens ; but the difficulty existed 
in finding some natural way of constructing and in accounting by 
known physical causes for the total demolition of the barriers, con- 
sidered as barriers of earth, whether of rock in siiic or of accumu- 
lated alluvia. He feels this difficulty acutely, it is evident, for al- 
though he may be said to have completed his subject, he still goes 
on, through a dozen quarto pages, to comment on the difficulties of 
this position and to offer explanations. "It is not, however, incon- 
ceivable," he says, " that the causes which are now, by the accumula- 
tion of alluvium, obliterating the existing lakes, should, under some 
variation of ground, have heaped a barrier on the course of a valley, 
and generated at one period a lake which they were afterwards de- 
stined to destroy, or which, accumulating strength by confinement 
while the opposed barrier was undergoing a slow waste, should sud- 
denly break its bounds and again desert the valley which it had been 
previously compelled to occupy" 
This, however, is an argument which carries its own conviction of 
