402 Proceedings of the Boyal Society 
sectional area — and the result is, that if we compare his own view 
with that which he ascribes to his opponents, the 133 : 1 is further 
diminished to 25 : 1. But there is a still more important fact to be 
taken into account. In calculating the sectional area of the old 
river the whole valley is assumed as empty ; but this it cannot have 
been, at least here in Scotland. If the rocky structure of the valleys 
was excavated, and the rock removed, how shall the floods be 
raised high enough to form the terraces? There only remain 
water and alluvium to fill the space. The only reasonable view is 
that the area of the valley was to a large extent occupied by masses 
of alluvium since removed. And this is borne out by what we 
actually find — fragments of old gravelly platforms left standing to 
tell of deposits which evidently were at one time far more extended. 
A third correction, not less important than the others, must be on 
this ground applied to Mr Prestwich’s calculation. So far from 
the valley having been empty, it must to a great extent have been 
filled with alluvial deposit since denuded. The difficulty raised 
as to the volume of the old floods is thus to a great extent set aside. 
At various points along the Spey — Kingussie, Coulnakyle, Crom- 
dale — transverse sections of the valley were given, showing the 
height of the terraces. From the width of the valley in these 
cases (of which details were given) it appeared that a calculation 
like that of Mr Prestwich in the Somme would bring out results 
equally incredible as to the old floods, hut owing to the above cor- 
rections this difficulty is removed, and the remarkable thing is that 
the 70 feet terrace at Kingussie has been laid open in an old river 
course, and the 80 feet terrace at Cromdale in a railway cutting so 
as to bring out similar results to those formerly shown from the 
valley of Monzie.* Explain the matter how we may, the river, 
with an open valley three-fourths of a mile wide, has begun at the 
bottom, on the level of its present bed, and piled tip these deposits 
to the height of 70 or 80 feet. That they are the work of the 
river is proved by the way in which the platform-like surface of the 
terrace slopes down the stream. 
The idea of ascribing these high-lying terraces simply to the 
greater flooding power of some former time was suggested by a 
comparison between the deposits of the Kuchil with those of the 
* Trans. Roy. Soc. Ed., vol. xxvi. pp. 171, 172. 
