264 
ME. PRESTWICH ON THE GEOLOGY OF THE DEPOSITS 
from the river*. Kespecting the upper part of these valleys, MM. Sauvage and Buvig- 
nier remark that beds of sand and gravel cover the hills which border the valleys, at 
levels far above the present rivers f ; and M. Buvignier has described beds of gravel 4 to 
6 feet thick, with remains of Elephants and other animals, at heights of from 100 to 130 
feet above the Aire, and 160 to 200 feet above the Chee, the Ornain, and the Saulx J. 
It is therefore certain that at points more or less distant along the course of all the 
rivers in the South of England and the North of France §, detached and isolated beds of 
sand and gravel occur on terraces, or on the top or shoulders of the low hills or plat- 
forms bordering the valleys, at various and often considerable heights above the present 
river-levels. Another and more continuous stream of gravel stretches along the bottom 
of the valleys. Beds of Loess cover both gravels irrespectively, and extend beyond them. 
It is in these deposits only (caves excepted) that the flint implements have hitherto been 
found. 
§ 3. HIGH- AND LOW-LEVEL VALLEY-GRAVELS. 
From the constancy of the phenomena described, we may arrive at a general pro- 
position which can be expressed by the following diagram (fig. 9) and terms : — 
Fig. 9. 
M. General section of the ground. 
D. Major valley of denudation anterior to the 
excavation of the valley C. 
C. Minor valley of river- excavation. 
A. Present river-channel. 
e. Non-fossiliferous drift on the slopes and base of 
the major valley D. 
d. High-level valley deposits 1 
t , . „ , l with or without fossils. 
c. Low-level valley deposits J 
a. Recent alluvium. 
This diagram represents the conditions of the case on the supposition that all the parts 
are complete. But this rarely happens. The gravel along the base of the major valley (D) 
is spread out or contracted according to the width, depth, and shape of its channel. If 
the secondary valley C should extend on either side beyond the limit of the beds e or d 
deposited along that first depression, the section would be represented by diagram fig. 10, 
where, as at Amiens, the hills on one side are completely denuded, whilst on the other 
side a portion of d remains. Or it might happen, as is the case in many parts of the 
valley between Amiens and Abbeville, also in the valley of the Oise near Creil, again in 
the valley of the Seine near Paris, and commonly elsewhere, that the width of C exceeds 
that of the first-formed channel characterized by the drift e and d, in which case the 
river-valley would pass through bare hills denuded of all traces of e and d, as in the 
* Mem. de la Soc. Geol. de France, vol. v. pp. 190, 193 (1842). 
f Statistique Miner, et Geol. du dept, des Ardennes, p. 58 (1842). 
t Geologie du dept, de la Meuse, pp. 95, 96 (1852). 
§ I restrict my remarks to this area ; but the fact has a much wider application. 
