The President’s Address. 17 
bison was intermediate between the existing bison of America and 
theEuropean aurochs. The next consideration on which the antiquity 
of these remains depends is the nature and position of the river 
gravels in which they are found. These gravels have evidently been 
formed and deposited by the rivers themselves where they ran at a 
higher level, that is to say, before they had excavated their valleys 
to the present depth. Even at that time the areas of drainage, at 
least of the principal rivers in question, for instance the Somme, the 
Seine, the Oise, the Thames, &c., were the same as now. This is 
proved by the fact that the pebbles which constitute the gravels are 
always such as might have been derived from the area of drainage. 
Thus the gravels of the Somme are made up of flint pebbles, the 
district drained by that river being entirely a chalk area. But if 
the river during the Paleolithic period had extended only six miles 
further inland, it would have entered upon an area containing rocks 
of earlier periods, fragments of which must in such a ease have 
formed a constituent part of its gravels. This consideration is very 
important because it shows that the valleys must have been excavated 
by the present rivers; and even admitting that from the then con- 
dition of the climate and from other considerations floods of that 
period may have been both more frequent and more violent; still 
the excavation of the valleys must have been due to the rainfall of 
each respective area, and thus not ascribable either to one great 
cataclysm or to the fact of the rivers having drained larger areas 
than at present. In many cases the excavation of the valley is even 
greater than might at first be supposed. The valley of the Somme, 
for instance, is forty feet deeper in reality than its present form 
would indicate, the river having filled it up again to that extent. 
The valley itself is from 200 to 250 feet in depth, and although this 
affords us no means of making even an approximate calculation as to 
time, still it is obvious that to excavate a valley, such as that of the 
Somme, to a depth of 250 feet, and to fill it up to the extent of 30 
or 40 feet with sand, silt and peat, must have required a very con- 
siderable lapse of time. Passing on now to the question of climate, 
it will be observed that the assemblage of mammalia to which I 
have already referred, is remarkable in several ways. It is interesting 
VOL. XVII.—NO, XLIX. c 
