356 Superficial Gravels and Clays. [July* 
The level at which these deposits began to be the 
rule, instead of the exception, was at about 120 feet above 
the Ordnance datum-line. Below this level they were spread 
out over all the flat or gently sloping ground, and only on 
the steeper gradients did not find a lodgment. As the water 
still further fell it drained into the old pre-diluvial smaller 
valleys, and in some cases the gravels have been swept out 
of these for some distance above the levels of the present 
brooks. The gravel and sand being all in motion together, 
there was a rough sorting of the materials, according to their 
weight ; the largest and heaviest stones found their way to 
the bottom, whilst the sand was more generally distributed 
near and at the top of the gravel. 
Pre-diluvial man had left his stone-implements around 
his old settlements, and many of these were mixed up with 
the materials brought down from the west by the flood and 
deposited with them, the larger flint-implements sinking to 
the bottom along with stones of the same size. At still 
lower levels many of the implements were not moved far 
from where they had been left on the surface, and in some 
instances were not moved at all. Above the 40-feet contour- 
line the bones of the large mammals that may have been 
lying on the surface deposits before the debacle, have been 
mostly swept away, excepting where preserved in hollows 
from the violence of the flood. A few of the large heavy 
teeth of the mammoth have been found in the gravels of the 
Ealing district, but the lighter bones are absent. In 1875, 
in digging gravel at the site of the New Museum of Natural 
History, at Kensington, the tooth of a mammoth was found 
at the base of the gravel, within 6 inches of the surface of 
the London Clay. No other bones occurred with it. A little 
farther west, in diggingthe foundations for houses in Crom- 
well Road, many fragments of bones belonging to the great 
ox, the red deer, and the mammoth were found near the top 
of the gravel, but none of the heavier teeth. It would 
appear from this that the remains were, like the stones of 
the gravel, deposited according to their specific gravity. 
Below the 40-feet contour-line, in the Brentford district, 
mammalian remains are most abundant. The reason why 
they should have been preserved there, is apparent when we 
look at a map showing the contour-lines of the district. To 
the west of Brentford, a spur of high land, all above 70 feet 
above the sea-level, comes down from Southall, as far as 
Hounslow. To the east of this the 50-feet contour-line 
runs to the north from Brentford, up past East Adton, to- 
wards Wormwood Scrubs, forming an inlet protedled from 
