CONTAINING FLINT IMPLEMENTS, AND ON THE LOESS. 
265 
Fig. 10. 
diagram fig. 11. Or the various gravels may also have been wanting originally, as there 
must have been parts of the old river-bed always left bare. 
Fig. 11. 
It is therefore not essential to the case that the high-level valley-gravels d should be 
permanent or continuous in the direction of their length. We have seen that they are 
generally found at heights above the river of from 50 to 150 feet, though occasionally 
more or less. The low-level gravels, on the contrary, often have even their upper ter- 
races so little above the level of present inundations that they might be attributed to 
such recent causes. The coincidence, however, arises from merely local conditions, and 
we can hardly apply to them a different rule, the more especially as, although the level 
of the terraces may be at places so low as to merge in the gravel at the bottom of the 
valley, still they even then form a breadth and mass of deposit which indicate a very 
different power to that now in operation in the existing rivers. 
That the formation of the higher terraces can be owing to the action of the present 
rivers is clearly impossible under existing conditions ; for they are far above the level 
reached by the rivers at the highest floods. 
Taking the mean depth of the Waveney near Hoxne at 3 feet and its width at 33 feet, 
whilst the depth of the valley between the two gravel terraces is about 40 feet and the 
width 2000 feet, the sectional area of the former will be 100 square feet nearly, whereas 
the latter will be represented by about 80,000 feet — in round numbers as 1 : 800. The 
Ouse at Bedford has an average depth of 5 feet and a width of 200 feet, or a sectional 
area of 1000 feet. The valley at the same point gives us about 12,000 feet — or as 
1 : 600. The rise of these rivers above their ordinary level never exceeds a few feet. 
Very little is known of the discharge of either river during floods*. 
If we take the Somme at Amiens at 4 X 200, the sectional area is 800 feet, whereas 
the valley at the level of the St. Acheul gravel gives 80 X 5000, equal to a sectional area 
of 400,000, or as 1 : 500. The floods of the Somme rarely exceed 5 feet above its mean 
level. Taking the Seine at Paris at a mean width of 600 feet and a depth of 4 feet, the 
sectional area is 2400 feet. The valley between the heights of Gentilly and of Charonne 
The numbers in this and the next paragraph are only approximately correct ; exact data are wanting. 
2 o 2 
