ALLUVIUM COVERING DILUVIUM IN HOLLAND. 
189 
modern rivers which is so enormous in that country, never rises above 
the level of the highest possible land floods; but beneath this level 
forms nearly the entire surface of that low and extensive flat; whilst 
the diluvial deposits rise from beneath it into a chain of hills, com¬ 
posed of gravel, sand, and loam, which cross Guelderland, between 
the Yssel and the Rhine, from the south-east border of the Zuyder 
Zee, to Arnheim, and Nymegen, and form at the latter place a cliff 
overhanging the left bank of the Waal, and another cliff of the same 
kind on the right bank of the Rhine, from Arnheim to Amerongen 
on the road to Utrecht. In the districts that lie below the flood- 
level of these rivers, it is probable that there is an extensive deposit 
of this same diluvium buried beneath the alluvium, which forms the 
surface; and the certainty of this fact has been established in several 
places, where, from the bursting of dykes, the water has made exca¬ 
vations through the alluvium into the subjacent diluvium, and washed 
we sometimes find a considerable talus-shaped accumulation of postdiluvian gravel, par¬ 
tially filling up the diluvian gorge of the transverse valley, and protruding itself to a con¬ 
siderable distance into the main trunk of the longitudinal valley; many striking examples 
of this latter kind may he seen in ascending the passage of Mont Cenis on its western 
side from Aiguebelle upwards. Here, at the termination or mouth of the transverse 
valleys that fall into the main valley of the Arc, immense talusses of gravel of modern 
origin project into the latter valley, being often incumbent on, and easily distinguishable 
from, the subjacent beds of diluvial gravel, and sometimes protruding across the great 
longitudinal valley, so as entirely to obstruct it, with the exception of a small passage 
which is kept open by the present river, in the lowest edge of the talus. I have seen also 
similar examples well displayed at the mouths of the transverse valleys, that fall into the 
main valley of the Kiszueza River, on the Hungarian side of the pass of Iablunka, at the 
west extremity of the Carpathians. Deposits of this kind go on accumulating daily under 
our observation, and may, by careful investigation, be always distinguished from that 
gravel which is strictly diluvian. All the cases above quoted rest on my own personal 
observations. 
