Bae aren 
ee ee 
as 4 
304 A, Tylor on the Amiens Gravel. 
Third, that the gravel in the valley of the Sonlie re 
Amiens is partly derived from débris brought down by the 
River Somme and by the two rivers, the Celle and the Arve, 
and partly consists of material from the adjoining higher 
grounds, washed in by land-floods,—the immense quantity of 
chalk present in the gravel having been derived from the latter 
source. It is where the surface of the chalk is concave that 
the gravel is thickest. 
= 
Fourth, that the Quaternary gravels of the Somme are not 
separated into tavo divisions by an escarpment of chalk parallel 
to the river as has been stated. They would have formed an 
exception to other river-gravels if this had been the case, The — 
St.-Acheul gravels thin out gradually as they slope from the 
high land down to the Somme, and they pass away into the 
Loess formation,—and so also at Montiers. 
The Loess deposit, on the contrary, forms a distinct escatp- 
ment for many miles along the Somme ; and this, I believe, 1s 
the bank of the ancient river whose floods produced the St- 
Acheul and Montiers gravels. 7 
Fifth, that the existence of river-floods, extending ® 
height of at least eighty feet above the present level of the 
Somme, is perfectly proved by the gradual slope and conte 
nuity of the gravels deposited by those floods upon the slopmg 
Beds of gravel, brick-earth, and loess, having ap.even clopig : 
surface from the escarpment of the sides of the valley aoe 
the terrace near the river-bank, are often to 
Sixth, that many of the Quaternary deposits in all me . 
se ; . and wher 
valleys that the Somme river bears to its ene foot above 
clearly posterior to the formation of the valleys in wile mu 
nm \ 
jn that they 
rr different ft 
have been formed under physical conditions very att 
must have immediately preceded the true Historical aa 
; 5 | é 
