CONTAINING FLINT IMPLEMENTS, AND ON THE LOESS. 
271 
lower gravels have a more washed, sorted, and worn character than the upper gravels, 
although there is in these also a certain proportion of angular materials. 
As the various Eocene, Miocene, or Pliocene strata spread over the South of England 
and North of France prove that, at some comparatively late geological period, the sea or 
large lakes extended over that area, it follows as an almost necessary consequence, that, 
when the land rose from beneath those seas or those lakes, a mass of debris, in quantity 
and length of transport proportionate to the greater or less rate of elevation and the 
depth of the superincumbent waters, must have been spread over the bottom of the 
channels along which the water flowed off; and assuming the rise to have been tolerably 
uniform over considerable districts, the course of the currents would be influenced by the 
form the land assumed during its emergence, or in fact by the present watersheds, which 
either result from or else bore part in that operation. In either case the ultimate effect, 
so far as our position is concerned, would be the same. That this must have been a 
vera causa to a certain extent is manifest, inasmuch as that which was sea or lake is 
now dry land ; and although it will not explain the origin of all the high-level gravels, 
there is a certain proportion of these beds which may nevertheless have this older and 
independent origin* : it is to be distinguished by rising higher up the hills, and not 
being restricted to so definite a level as some of the other beds. I have reason to believe 
that some of the gravels in the South of England and the higher levels of the Somme 
valley may be of this age, — such as those above Epagnette, and the higher levels of 
those above Breilly and Montiers. In proof of the existence of some gravels older than 
those of St. Acheul and yet belonging to the Somme valley, I would mention the not 
uncommon occurrence at that place of subangular flints, with a deep brown staining, 
imbedded in layers of perfectly white gravel. As this discoloration can only arise from 
the flint having been imbedded at some time in an ochreous or ferruginous matrix, I 
infer that such specimens are derived from beds of gravel of that character, and older at 
all events than the St. Acheul gravels. As a proof of their staining being clearly 
unconnected with any colouring-matter of the existing matrix and being of older origin, 
I noticed that they have all had a second rolling, and that where their first angles have 
been worn off and the outer brown coat removed, the eroded surfaces often show, first 
an original white crust, and then the black core of the flint, without any change of 
colour on these fresher surfaces due to their present position. 
The theories that have been formed to account for the entire series of these valley- 
gravels by the bursting of lakes, by the sudden melting of the glaciers and snow of 
mountain-regions, or by the transitory passage of any body of water over the land, are 
open to objection, because the debris would have been swept along in fewer and more 
definite directions, or would have held its course more irrespective of the existing water- 
sheds, and would have shown an amount of wear in all cases proportionate to the dis- 
tance travelled. Not only is this not the case, but the condition of the fragile shells 
* Another portion of the high-level gravels must have been formed before the country became inhabited, 
and would therefore also be unfossiliferous. 
MDCCCLXIV. 
