FROM THE CHALK OE HERTFORDSHIRE. 
149 
Colne watershed, and percolates to these layers of flints, must he 
carried along them beneath the catchment-basin of the Lea; and 
I think there can be little doubt as to the correctness of the con¬ 
clusion which Mr. R. Ab. Mylne arrived at from a long and careful 
study of the underground waters of this district, in his capacity of 
Engineer to the Hew River Company, that the water absorbed in 
the swallow-holes at Potterells is completely lost to the Colne, 
being conveyed underground to the lower portion of the valley of the 
Lea. It was his opinion that the Amwell Spring and other springs 
in its neighbourhood were thus fed, but to be certain of this we 
require more conclusive evidence than he has adduced. He was 
convinced that “no large supply of underground water can be met 
with, within a moderate radius of London, without diminishing the 
minimum, or dry-weather, flow of the streams.”* 
The point of practical interest to us is that the pumping of water 
from great depths in the valley of the Lea between Hoddesdon and 
Tottenham may drain the Colne and its tributaries almost as much 
as the Lea and its tributaries. At Hew Southgate, near Barnet, the 
nearest point to the head of the Colne at which the Hew River 
Company has a pumping-station, nearly all the water drawn is 
probably derived from the rainfall in the upper portion of the 
Colne valley, most of which, as we have seen, disappears from the 
surface at Potterells and in numerous swallow-holes in the bed of 
the river above that point. This question, however, properly 
belongs to the next division of our subject, the Abater-supply of 
London. 
The configuration of London and its suburbs has been mainly 
determined by the presence of the water-bearing alluvial gravels 
which rest upon the London Clay in the valley of the Thames. 
Rain falling on the surface of the ground permeates and saturates 
these gravels, being held up by the clay, so that it was at one time 
only necessary to sink a well a few feet in depth in order to obtain 
a supply of water. Abhere, also, the gravel was cut through down 
to the London Clay by shallow valleys, springs then issued forth, 
whose waters are said to have been, in the reign of Henry the 
Second, “ sweet, salubrious, and clear.” Abith an increasing popu¬ 
lation, and with no drainage but that which cess-pools afforded, these 
sources of supply gradually became contaminated, but were used, 
with very prejudicial effects, after they had ceased to be sufficient, 
and recourse to outside sources had become absolutely necessary. 
Even as early as the year 1236 “ the citizens were forced to seek 
sweet waters abroad,” and water was conveyed “from the town of 
Tie Burn [Tyburn] by pipes of lead into the City,” but most of the 
water required for domestic purposes was brought in buckets from 
the Thames. 
In 1582, and for 240 years afterwards, water was pumped from 
the Thames by water-wheels worked by the tides in the arches of 
old London Bridge, and conveyed by pipes first to a small area in 
the City and in course of time to all parts of London. 
* See ‘Report Brit. Assoc, for 1890,’ p. 353. 
