9 
and its banks, protected by vegetation, scarcely experience any 
modification/* * 
Belgrand, from a consideration of tbe physical phenomena of 
the Seine valley, concludes that the valleys were scooped out by 
waters of flooded rivers running at the highest levels of the 
gravels by a process far more violent than the present forces, 
and that they were by the same process filled with gravel from 
the destruction of the surrounding beds, and then again scooped 
out by floods which continued long enough to produce great 
rushes of water from the plateaux above, down into the valley 
whilst and after it was thus again excavated.f The section at 
Eisherton, near Salisbury, given by Mr. Evans in the 
Quarterly Journal of the Geological Society, vol. xx. p. 191, 
shows exactly the state of things. High up under the 
brow of the hill, 80 feet above the bottom, is a patch of 
gravel lying in the cheek of an eroded hollow in the 
chalk ; lower down is another patch which passes under 
the present small stream. In both are there flint instruments, 
and in both are there mammalian remains of the mammoth 
age. Difficult as it is to imagine that the mammoth could 
have resorted to the river-banks, and man pursuing it at 
intervals during an excavation of 80 feet, yet this is the fact 
deducible from the evidence ; and it is equally deducible that 
this excavation was not caused by the slow operation of present 
forces, but by some means incomparably more rapid and effective. 
Mr. Prestwich tells us : “ That the rivers were larger and 
more rapid than now, is evident from the great quantity of 
debris, the prevalence of the gravels, the coarseness of the 
sands, and the general absence of mud sediments/* . . . “ The 
melting of winter snows, and combined possibly with a larger 
rainfall, must have afforded to the old rivers a volume of water 
far exceeding any present supply, and giving them more of a 
torrential character.** It appears, therefore, that the gravels in 
these rivers are part of the phenomena of their erosion. 
Original inequalities and lines of depression became the 
natural channels of running water, the latter in flood erodes 
the substratum, washes away the lighter materials, and grinds 
and sorts the pebbles; thus forming gravel and sand. After 
this process had gone on to nearly the present levels, and 
during some part of the time, and when the action was still 
intermittent, man followed the mammalia into these parts. 
What we have, therefore, is violent diluvial action, under the 
influence of which the valleys were formed in pre-existing 
* Leisure Hour, 1874, p. 767. 
t La Seine, p. 99. 
