of Edinburgh, Session 1870-71. 
405 
Nor can it be said that the submergence of Scotland as con- 
trasted with the area of the Somme, which was not submerged, can 
constitute the difference, for Mr Prestwich has shown * not only 
that the French system of valleys has crossed into the south of 
England, but that it prevails indifferently as much beyond as within 
the line of submergence traced by Sir 0. Lyell. That submergence 
seems in this respect to make no difference. 
It is equally in vain to allege that the large amount of alluvium 
in the Scottish valleys makes such a ground of distinction when 
contrasted with the lesser amount of such deposits on the Somme. 
The alluvium along our Scottish streams is a very variable quan- 
tity as between valley and valley, and as between different portions 
of the same valley. On the other hand, the amount of the Somme 
gravels at Amiens and above it, is great — so great, that both Mr 
Prestwich and Sir Charles Lyell argue in favour of their antiquity, 
from the length of time which must have been needed to accumu- 
late such a volume of debris. On the Oise also, and some neigh- 
bouring streams, the amount of alluvium is described as very great. 
It is enough, however, to remark, that the burden of proof lies 
with the advocates of antiquity, and that its difficulties have not 
been surmounted. On the other hand, there is one thing which they 
may fairly be asked to do — if they maintain that the French and 
Scottish valleys have been formed on different principles — to show 
where the two systems meet. The French method, as we have 
seen, crosses into England. No one will maintain that the Scottish 
stops at the Tweed. Somewhere they must come in contact. It 
would be instructive if some one would try to show us two conter- 
minous vp^eys wrought on the opposite plans. The attempt would 
probably evince the impossibility of drawing such a distinction. 
In all that is important, the French and Scottish valley systems 
go together. 
The whole of these remarks are submitted as suggestions, show- 
ing the need of much more complete investigation. On this whole 
series of deposits we have much to learn, — far too much to admit of 
anything like confident conclusions being drawn as yet. The only 
safe course is to await the results of future research. 
* Phil. Trans., vol. cliv. PL iv. 
t Prestwich, ut sup , 286. Sir C. Lyell, “ Antiq. of Man,” p. 144. 
3 r 
VOL. VII. 
