34 THE SHALLOW AND DEEP WELL WATERS OF ESSEX.
since only been used for slopping purposes. What caused this
change ?—the deepening of the well, or the process of shelling, which
may have destroyed the continuity of the tube and allowed water
from some source at a lesser depth to enter? This is a question
upon which I should like to have your opinions.
My analyses of the deep well waters are divided into three
groups.
1. Those of waters not exceeding 5" of hardness.
2. ,, with a hardness of over 50, but not
exceeding 10".
3. „ with a hardness exceeding 10o.
(I may here remark that the depth of the wells given in Col. I. are
almost all taken from Mr. Whitaker's Sections, and that it is toler-
ably certain that the water from the wells of unknown depth is from
the Tertiary sands.)
In each of the three groups we find waters from both the chalk
and sands, and it is impossible to tell from the analyses from which
source the water is obtained. Take, for instance, the first group,
Table III., the waters from the very carefully made wells of the
Southend Waterworks Co.—wells sunk expressly to exclude all water
except that coming from the chalk. Compare these with the water
from the Tertiary sands at Woodham Ferris, Rettenden, and
Runwell. All contain very small quantities of lime salts, and a
considerable amount of chloride and carbonate of sodium. At
Brentwood, and south of Brentwood, however, the soft chalk waters
contain much less salt (vide, waters from Brentwood Asylum, Pyrgo
Park, and Britannia Works, Ilford). A few of these waters contain
a larger quantity of sodium chloride than the others, more espe-
cially the chalk water at Tiptree Brewery, and the sand water at
Bridgewick Farm, Dengie. The latter is close to the sea, the
former many miles distant. The soft waters obtained near Maldon
also contain an excess of salt; but the wells here are close to a tidal
basin. If the salt, however, be due to infiltration of sea water, how
is it we obtain no indications of the presence of magnesia ? I may
also draw your attention to the fact that nearly all these soft waters
are exceptionally pure, as indicated by the small quantities of
nitrates present.
When we examine the second group (Table IV.), we find there
are only three chalk waters (two at Colchester and one at East
Donyland, near Colchester). These differ somewhat in character.