354 TJie American Geologist. December. i898 
small ponds, or moats, as they would be called in New Eng- 
land, occupy these hollows, and in other places mark aban- 
doned parts of the earlier river channel. Since the close of 
the Glacial period, the Somme valley has received too little 
alluvium to keep pace with the slight epeirogenic depression 
which has been in progress; but at the mouth it has been 
filled by the coastwise drift of sand from the marine shore 
erosion, and by the muddy sediments deposited from inflow- 
ing tides. 
On each side of the valley the upland extends far away in a 
great plainlike expanse, as seen in any wide view, though 
everywhere somewhat undulating, with an elevation of 150 to 
250 feet above the river and its bottomland. Rounded out- 
lines descend to the Somme and to the ramifying tributary 
streams, betokening a prolonged period of subaerial denuda- 
tion by rains, rills, brooks and the main river, quite unlike 
the sharp-crested blufifs eroded, for example, in the glacial 
drift along the similarly deep Minnesota river valley and other 
valleys cutting thick drift plains in the upper part of the Mis- 
sissippi basin. The Somme, lying south of the European 
glaciated area, has in its gravel deposits only materials de- 
rived from its own drainage basin, which consists of approx- 
imately horizontal Cretaceous strata of chalk, with concre- 
tionary flint nodules, and here and there overlying remnants 
of Eocene sand and clay, locally hardened to sandstone and 
shale. Residuary clay or loam, left in the process of detmda- 
tion, covers the upland surface to a depth varying generally 
from two or three to six or eight feet. 
The erosion of the Somme valley to essentially its present 
width and depth seems to me attributable to the work of the 
river during the very long Miocene and Pliocene periods, 
and to have been completed nearly as now before the great 
epeirogenic uplift causing the Ice age, which probably raised 
the British Isles and northern France at least 1,500 feet to 
2,000 feet higher than now, while southwestern France and 
the Spanish peninsula appear to have been elevated mucli 
more. The evidences of this very great general uplift of 
western Europe were stated in the seventh paper of this 
series.* The record of the Glacial period here appears, in 
*Am. Geologist, XXII, 101-108, August, 1898. 
