24 Reviews—Prestwich on Valley-Deposits. 
winter-temperature was at first considerably lower than at present, 
but the severity of which was being gradually mitigated. The 
volume of water that there must have been in the old rivers (which, 
it will be remembered, had no greater gathering ground than their 
representatives of the present day) to spread out such masses of 
coarse shingle may be safely assigned to the greater winter-accumu- 
lation of ice and snow, which must of necessity have accompanied a 
greater degree of cold, and which by rapid thawing in the spring- 
or summer-months would periodically cause immense inundations ; 
while the transported blocks, scattered indiscriminately through the 
gravel, and often associated with delicate and fragile shells, and with 
mammalian bones but little if at all rolled, can hardly be referred to 
any other action than that of ice, to which also the contortions in 
the gravels already mentioned appear to be due. The excavating 
powers of rivers in such a climate would, owing to the torrential 
character imparted to them by the summer-thaws, be far greater than 
at present, even were the rain-fall the same; but it is by no means 
improbable that, in the neighbourhood of the sea, the greater cold 
would be accompanied by a greater precipitation of rain or snow. 
But besides the mere excavating power of the running water, Mr. 
Prestwich calls to his aid the operation of ground-ice (which he 
shows to be a powerful transporting agent), and the effects of alter- 
nate frosts and thaws in breaking up masses of rock, and of the 
solvent powers of rain and snow-water. And he further invokes 
the assistance of the gradual upheaval of parts of Kngland and 
France, of which we have some evidence in the raised beaches which 
in places fringe the shores. 
Into all these questions we have not space to enter; but we think 
we have said enough to show the interesting character of this Paper, 
and to give some idea of the array of facts on which Mr. Prestwich’s 
theory is based. It will be seen that, while he entirely abjures the 
cataclysmic theories still held with regard to these river-gravels by 
so many French geologists, he is reluctant to attribute the entire 
excavation of the valleys to causes operating with no greater inten- 
sity than they do at the present day. Yet we think that the ‘Quietist’ 
need hardly regard such views with distrust, nor the ‘ Catastrophist’ 
hail them with satisfaction as supporting his opinions. For after all, 
granting, as there seems no reason to doubt, that we had in this part 
of Europe at the commencement of the Post-pliocene period an Arctic 
temperature, it is evident that during the transition from such a 
temperature to that which prevails at the present day, there must 
have been a time when conditions such as those which Mr. Prestwich 
describes prevailed, and during which the ordinary excavating forces 
of rivers must, in the course of Nature, have operated with greater 
intensity than at present. It appears to us not impossible that the 
excavation of the valleys above the line of the high-level gravels 
containing organic remains, and which Mr. Prestwich seems inclined 
to attribute in some measure to the action of the sea during the 
emergence of the land from beneath it, may have taken place during 
such a subglacial period. At all events, if the land were above 
