THE GEOLOGY OF LONDON. 
9 
of tlie palseolithic (older stone) period, the mind is almost lost 
in amazement at the vista of antiquity displayed.” * 
When we come, however, to discuss these subjects, we begin 
to trespass on the province of the archseologist, and we must 
leave them to consider a few more points connected with 
geology. 
Mr. Prestwich f has shown how the earliest settlements in 
and around London were dependent upon the geological struc- 
ture, and for this reason. The London clay which occupies so 
large an area is, as we have mentioned, covered to a large ex- 
tent by the valley gravels, and in the north of London by here 
and there an outlying hill of Bagshot sand. Wells sunk through 
these sandy and gravelly deposits were always supplied with 
water, which was kept up by the impervious London clay. 
Hence as the water supply was an all-important question with 
the early settlers, so they followed the course of the water- 
bearing strata, while the bare London clay was unoccupied 
until the New Eiver and other water-works did away with the 
necessity for wells. Thus the clay districts of Holloway, Camden 
Town, Eegent’s Park, St. John’s Wood, Westbourne, and Not- 
ting Hill received town populations much later than Stepney, 
Hackney, Islington, Kensington, Chelsea, and Camberwell, 
which are situated on gravel. 
In the same way, Mr. Prestwich has pointed out how on the 
outskirts of London a succession of villages grew up for miles 
on the great beds of gravel, ranging on the east to Barking, 
Ilford and Eomford ; on the north, following the valley of the 
Lea to Edmonton and Hoddesdon ; and on the west, up the 
Thames valley, to Hammersmith, Ealing, Hounslow, and be- 
yond. Around Harrow, which stands on the Bagshot sand, a 
large area of bare London clay extends, which is remarkably 
free even now from the encroachment of houses, particularly 
between Harrow and Ickenham on the west, and Edgware on 
the north-east. 
When the supply from the shallow wells through the valley 
gravels was found insufficient to furnish the demand for water, 
deeper wells were sunk through the London clay into the 
sands beneath and into the chalk, which hold a great quantity 
of water. Owing to the outcrop of the chalk both to the 
north and south of London, forming, as we have mentioned, 
the London basin, this formation receives a quantity of water 
from the rain-fall which, percolating through it, is sustained by 
the clayey beds at its base, and is prevented from rising up in 
the centre of the basin, owing to the covering of London clay. 
* “The Ancient Stone Implements, Weapons, and Ornaments of Great 
Britain.” By John Evans, F.E.S., &c. 
t Anniversary address to the Geological Society of London, 1872. 
