The gravel is 13 feet thick at the Rue de Cagny, nearly 20 
feet thick in the St.-Acheul pit, and runs out to 6 feet at the 
_ Railway-works ballast- and chalk-pit at the escarpment. 
ve no section of gravel further north than this pit. 
If a straight line be drawn from the Rue de Cagny to the 
; @, along the line L M, it passes the Imperial Road on the 
level, and is 15 feet below the surface at the Railway-works 
ast-pit; so the surface is convex at that point. 
The convexity of the chalk on the same line is 14 feet at the 
ballast pit. 
__ Section N O P.—Plate IV, fig. 8.)—This section commences 
tthe Ferme de Grice, point N, at a height of 201 feet above 
ane sea, and goes along the road to Montiers by the line NO P 
: as far as 0. The first gradient is 1 in 33, north; 1 in 90, lin 
5 70,1; in 105, 1 in 110, 1 in 110, 1 in 110, 1 in 57, 1 in 60, Lin 
4. 00. Here it crosses the junction of two roads at a 
Taek of 155 feet above the sea, "Then follow on north 1 in 60, 
27, Lin 40, 1 in 60, to the point O, at a height of 120 feet 
to th sea; then 1 in 30 and 1 in 75 to the railway, 1 in 33 
‘Go € Imperial Road, then 1 in 56, 1 in 50, 1 in 231, and it 
“above the top of the escarpment of loess at a height of 81 feet 
iB “sage sea. ‘Then the ne of escarpment falls 162 feet in 
ot then is horizontal to the river. 
states be drawn from the Point N to the river Somme 
ce ne 
¢ i 
: 4 
2 
u 
| 
? 
; 
. 
be 
: 
: 
me by previous writers 
ft ghetto of chalk at the junction of the two roads is 142 
mig", through NO P. 
feet below a straight line drawn from the Ferme de 
t above the sea to the Somme (at a height of 61 
