CONTAINING FLINT IMPLEMENTS, AND ON THE LOESS. 
273 
exactly proportioned to the accumulation of river sediment and to keep out the sea is 
very difficult to imagine, and is certainly not supported by the facts. 
What I propose to show is, on the contrary, that the brick-earth is intimately associ- 
ated with all the valley-gravels and is contemporaneous with and dependent upon them 
from the beginning to the end of the series, the higher deposits having been formed 
before the excavation of the valleys, and those on the lower terraces being of later date. 
I have said that in the valley of the Somme the high-level gravels rise to the height 
of 100 feet above the river; and from some recent observations I conclude that there are 
some beds which attain a height of 150 feet. Now, if we take this latter level as having 
been the floor of the valley through which the river flowed at the period when these 
gravels were deposited, we shall find the Loess still extending to about 60 or 80 feet 
above such a plane. At the same time we know that the greater portion of it is accu- 
mulated in irregular masses on the slopes of the hills at a still lower level, where it 
either reposes immediately upon the chalk substratum or else covers the low-level 
gravels. In the adjoining valley of La Bresle I found traces of the higher gravels 40 feet 
above the river, and the Loess, with Pupa &c., rising to 110 feet above this level. 
In the valley of the Oise, near Creil, I noticed traces of gravel on hills 65 feet above 
the river, whilst the Loess rises to a height of 115 feet. In the valley of the Seine I 
observed the high-level gravel at the Pont de 1’ Arche rising 140 feet above that river, 
and again the Loess 50 feet higher. In the neighbourhood of Mantes and of Rouen 
we found analogous phenomena. The great height to which the Loess rises in the 
neighbourhood of Paris has often been remarked upon by the French geologists, and 
its occurrence on the hills above Meudon has long presented a difficulty*. Its height 
there is about 320 feet measured by an aneroid barometer. It is perfectly well 
developed, is several feet thick, contains a few land shells, and presents all the cha- 
racters of the same material on the lower levels. M. Charles d’Orbigny has shown 
me the Loess rising up to the top of the hill above Ivry, and between the fort and 
Villejuif. It there attains a height of 305 feet above the river. These levels give a 
height above the high-level gravels of 150 to 200 feet, for at the Butte-aux-Cailles these 
are not more than 130 feet above the river ; but some gravels I observed on a hill- terrace 
near Mont Valerien may be as much as 150 to 160 feet above the Seine. Further search 
may also show the existence of higher beds ; or such beds may have been denuded. 
However much, in fact, the Loess may extend beyond the limits of the present river- 
valleys, it is always bounded by higher hills flanking the plains and the lower ranges. 
Thus, though it spreads over the low plains and hills of Belgium, it does not rise more 
than two-thirds up the flanks of Mont St. Pierre at Maestricht. In Kent it extends 
far up the slopes of the hills flanking the river-valleys, but it is in all cases bounded 
* This outlier of Loess has been represented as capping those hills. This would greatly increase the 
difficulty of connecting it with any old river-action, as it would extend the river boundaries to a compara- 
tively indefinite distance. Such, however, is not the case. High as it is, it is still at least 100 feet below the 
summit of the hill. 
2 p 2 
