of Edinburgh, Session 1870 - 71 . 
477 
Sir James Hall and Sir G-eorge Mackenzie in this Society, who 
were the first to study the subject, advocated the idea of diluvial 
agency. At a later period, ice in various forms was suggested as 
the agent,—First, in the condition of glaciers filling our valleys; 
next, in the condition of icebergs floating over our island, whilst 
under the sea; and latterly, as a great sheet or cake stretching 
from the Arctic regions, and overspreading the whole of northern 
Europe. 
It is not my intention to discuss these theories, or say which 
appears the most probable. I allude to them now, merely to in¬ 
dicate the tremendous character of the agencies, which it is found 
necessary to invoke for the solution of the problem,—agencies 
all implying a very different condition of things in Scotland, as 
regards configuration of surface and climate, from what now pre¬ 
vails. These phenomena are the more interesting, because, as 
most of the erratic blocks lie above all the rocks, and very frequently 
even above the beds of clay, gravel, and sand, which constitute the 
surface of the land we inhabit, they indicate probably the very last 
geological changes which occurred in this part of the earth’s sur¬ 
face, and which there are some grounds for supposing, may even 
have occurred since this country was inhabited by man. 
The basis on which geologists have been obliged to build their 
theories, it must be admitted, is somewhat narrow. It consists 
merely of observations made casually by individuals, who have 
noticed certain appearances in districts of Scotland which they 
happen to have visited; and, therefore, it is little to be wondered 
at, that more than half a century has been required for procuring 
the information, scanty as it is, which has been obtained. 
What appears desirable for expediting the solution of the pro¬ 
blem, is to organise a staff of observers, and to parcel out the 
country amongst them, for the purpose of observing facts likely 
to throw light on the subject, and of making these facts known 
from time to time, both with a view to verification, and as a basis 
for further speculation. 
It has occurred to me, that the numerous natural history societies 
and field clubs existing in Scotland, would be valuable agents 
in this investigation; and, moreover, that individual geologists 
would be pleased to co-operate in their respective districts. 
VOL. vii. 3 s 
