314 A, Tylor on the Amiens Gravel. — 
as the slope af the bottom is 1 in 40, nearly equal to the slope 
of the chalk itself at St.-Acheul, which is 1 in 33. This river 
is now dry, 
I ask particular attention to the position and level of this 
dry valley, which is similar in character to those occurring on 
all chalk-downs and plateaus. 
The chalk surface at St.-Acheul is also hollowed out intoa 
valley situated north of the Imperial Road, widening out as it 
approaches the Somme, after the ordinary manner of valleys. 
By the sections through the St.-Acheul pits, we know this 
valley did not extend south of the Imperial Road; but the 
eastern boundary of this small valley, only 400 or 500 
long, is well seen at the La Neuville Hastern Bridge, where the 
chalk is well exposed in the railway cutting, at a height of 20 
feet above the rails, and slopes westward, passing under the 
rails near the point C in the map, between the lines of section 
and L M. ; 
The surface of chalk is shown in a very clear section on the — 
railway here, covered with twenty feet of loess (fig. 11). The 
chalk is nowhere naturally exposed. The force of water fom 
St.-Acheul originally hollowed out this small valley m the 
chalk, which has been partly filled up with gravel and loess; 
and the surface-drainage of St.-Acheul flows to the vi | 
Somme down this valley, over a bed of gravel and loess © 
some thickness. ze 
There is a very small lateral valley in the chalk, running 
from St.-Acheul into the now dry valley at the western eye 
ment, also covered with loess and gravel, The slope © : 
side of this valley is as much as 6°. a 
Crossing over from the east of Amiens to the west, we ee 
to the section N O P, which gives us a correct view © 
surface of the chalk at Montiers, where fossiliferous 5™ 
were discovered by Mr. Prestwich. (Plate LV, fig. 7) 
The gradients have been already described. 
and O the surface of the chalk is slightly convex ; but 
r 
. 
. 
, 
between 
e itself, 
height. It is in this basin of the chalk that the great “iF 3 
beds of Montiers may be seen, in which 30 feet of eal Road. 
loess is well exposed, south of and close to the Imper’ yy 
The fossiliferous gravel extends above the railway + pout 50 
Prestwich found shells in a pit which appears toe | 
feet above the river at Montiers. ; ‘q distance 
The chalk is nearly horizontal beneath the rails for 4“ 
