439 
of torrents, and the more so as these two causes must of 
necessity have been conjoined, since it is evident that if vast 
masses of glacial ice formerly filled these valleys, there must 
have been numerous and powerful torrents consequent on its 
melting. This is indeed so apparent in many cases, that Dr. 
Buckland has adopted the term of " diluvio-glacial," to 
express the phenomena of Snowdonia, considering that 
glaciers were only one of several powerful agents in deter- 
mining the peculiar forms of rocks, and the distribution of 
blocks over vast distances from their original position. It 
has long been considered, that to powerful torrents from the 
north or north-west, are to be ascribed the transportation of 
rocks and shells over the western declivities of Snowdonia, 
and over various parts of Derbyshire and Shropshire. 
Floating ice-bergs are considered by the present President of 
the Geological Society to have been important agents, and 
torrents of a more local nature have doubtless been instru- 
mental in the great work of denudation. Whether to these 
agencies, — the evidence of which is beyond all doubt, as the 
vast accumulations of drift in this neighbourhood, and in 
various parts of Great Britain, abundantly testify, — that of 
glaciers is correctly added, is a theory which, if it cannot yet 
be considered as fully established, is at least supported by 
evidence sufficiently strong to merit further investigation. 
The groovings or large marks in rocks, similar to those 
which are formed by glaciers in Switzerland, are quite 
apparent on a vast number of rocks which I have examined, 
and I have never yet failed to find them in positions where 
they might be expected to be, if the theory of their being 
the record of the descent of a glacier is correct. In exposed 
rocks these groovings are often destroyed by the weather, 
which indeed is fatal to much of this kind of evidence, espe- 
cially in soft rocks. Hence it is only where a rock has been 
laid bare by a new road or a quarry, that a favourable oppor- 
