HISTORY OF COLCHESTER CORPORATION WATER WORKS. 27
contained no water I have never been able to ascertain,
except that it was unfavourably placed as regards elevation,
the chalk below being compressed due to the pressure of super-
incumbent mass above. The result of my experience is that
wells placed in the floors of valleys, yield water more freely
than when placed high up the flanks, or on the top of the
plateau; the reason appears to be that the beds are much
more broken up and fissured in the valley, and besides the
underlying chalk is not so compressed.
Nearly all the wells and bore holes which have been sunk in
the Borough and neighbourhood from the floor of the valley
yield water freely, and several of them are practically
artesian.
There is undoubtedly a large quantity of water travelling
from the outcrop of the chalk on the north-east, beneath the
floors of both the valleys of the rivers Colne and Stour, on its
way to the sea, that being probably the line of least resistance
due to greater Assuring and because the beds are less compressed.
It must not be lost sight of that the water does not travel
through the whole mass of the chalk, but along planes of
bedding, beds of flints, and through a network of vertical and
horizontal fissures. It also flows more easily down the dip than
across it on the way from the water-shed down to the lowest
point, which is the sea. It would be interesting to know whether
the water yielded by the wells in Colchester is derived directly
from the chalk outcrop to the north-west in Cambridgeshire
and Suffolk, or is connected in any way with the River Stour
between, say, Borely and Henny about twelve miles distant,
through which district the river intersects the open chalk.
Although the Chalk is of great thickness in East Anglia and
Essex, say about 850 feet, and is practically water-logged
throughout its thickness, it is only the Upper Chalk or porous
zone, say from 300 to 400 feet thick, which yields water in this
district. This Upper Chalk contains in its mass, locked up in its
capillary pores, so to speak, some two to three gallons of water
per cubic foot, which cannot readily be got out by pumping, but
only by pressure, and has been described as Capillary Water.
The water we obtain by wells and bore holes in the Chalk in
this neighbourhood is not this capillary water, but water flowing
in undefined channels and fissures.