312 A. Tylor on the Amiens Gravel. 
marly in color, often mixed with loess, and with ferruginow 
stains, When the chalk is quarried, the large masses fall 
down like boulders, and are used for purposes of masonry, — 
untouched by the quarryman. The hard pieces of chalk pro- 
ject beyond the soft matrix in which they are inclosed, like the 
flints upon the Brighton cliff, making a serrated face. The 
largest piece that has fallen out is only about three feet long, 
according to M. Dailli, who has quarried thousands of tons of 
chalk without meeting with a larger mass. There is a pipe, 
ten feet in diameter, in M. Dailli’s garden, and the depression 
in the chalk at the north-east corner has a pipe-like form. 
with great intensity on the high land adjoining, so that the 
current was from above downward, About one-eighth of the 4 
St.-Acheul gravel consists of chalk in the form of large pe® — 
averaging 4 inches diameter, of chalk pellets from $ t ya 4 
diameter, and of chalk finely divided and. mixed with clay. : 
ere we can see the chalk near C, it is so perforated bs 1 
pipes and separated into small pieces that it seems prepared 4 
a rapid denudation if attacked by water with any Vig0l, we [ 
if this was the condition of the chalk also at higher levels I 
St.-Acheul and Montiers, we can account for the large 4 
tity of chalk contained in the Amiens gravels. |, fifteen - 
The fall of the Somme from Longueau to Montiers18 wae 
feet, the river flowing from southeast to northwest iia Net 
a gradient of only 1 in 1520. The rails are 96 feet at 4 
ville, and 99 feet at Montiers, above the sea-level. sa 
By referring to the sections, CD, EF, GH, which are Ja 
lel with the river Somme and the Imperial road, } 
western escarpment of the chalk near the northern t ir 
of the Rue ste Cagny, the surface of the chalk 1s extremely 
regular and horizontal. : -; only 
The highest point of the chalk on the line © His 
feet higher than the lowest point on that line. ie of 
There is a steep escarpment, 50 feet high, at oats neat 
bare chalk facing the east, and an escarpment 30 feet: wee 
