258 
ME. PEESTWICH ON THE GEOLOGY OF THE DEPOSITS 
one, which more resembles the St. Acheul spear-head type. 
The deep discoloration and curious dendritic markings on these 
flints, their form (not upon the neighbouring St. Acheul type, 
but upon one before unknown to the men), and their small 
number preclude the idea of any collusion or deception, and 
substantiates the statement of Dr. Rigollot, that such imple- 
ments have been found in the like gravel at St. Roch*. On 
the hill rather higher than the new ballast-pit is another pit, 
where the gravel is shallower, contains no organic remains, and 
is probably of rather older date. 
The more general examination I have made of the Somme 
valley, from about six miles above Amiens, to the sea at St. 
Valery, a distance of forty-seven miles, has been sufficient to 
show the persistence of the same structural features. (PI. V. 
fig. 2.) In descending the valley below Amiens, after passing 
the gravel-pits of Montiers and Breilly, the chalk hills rise 
abruptly from the valley, covered only with more or less loam 
or brick-earth, except near Picquigny, where a few gravel pipes 
in the escarpment attest the former presence of a high-level 
gravel apparently 60 or 80 feet above the valley. On the hill 
which projects into the valley between Le Gard and Crouy is 
a capping of flint gravel. 
At Conde the valley-gravel again occurs, but thence by Fon- 
taine and Liercourt the hills present a bare surface of chalk, or 
else a capping and skirting of brick-earth only. At Mareuil, 
three miles south from Abbeville, and still on the left bank of 
the river, we find the gravel, capping, to a thickness of 6 to 8 
feet, the hills which rise behind the village to a height of 110 
to 130 feet. I could not discover any organic remains or flint 
implements f. From this spot to Mautort the chalk hills rise 
abruptly from the valley, either bare or more or less covered 
by brick-earth, but still showing here and there traces of gravel 
pipes, indicating the former existence of gravel beds at about the 
level of 80 to 100 feet above the river. Here also, as at other 
spots where the hills advance upon the valley, the depth of the 
latter seems to be greater, so that all the valley-gravel and Loess 
is covered up and hidden by the recent alluvial deposits which 
come close to the foot of the chalk escarpment. (PI. V. fig. 1.) 
* I have since had the opportunity of confirming the statement of Dr. Eigoilot, the men havin«- found four 
rude but undoubted flint-flakes at this spot (April 1863). 
f M. Boucher de Perthes has two specimens in his collection labelled as from this locality. 
Fig. 6 . — Section across the ValUy of the Somme near Abbeville. 
