36 THE SHALLOW AND DEEP WELL WATERS OF ESSEX.
much sodium chloride and carbonate. On the other hand, in the
central portions of the county the waters from the sands and the
chalk beneath are practically identical. (Vide also Whitaker's
"Geology of. London," vol. i., 514.) How are these differences and
agreements to be accounted for ? What is the source of the
carbonate of sodium found in both the sand and chalk waters
throughout the county ? Possibly the water under the central and
eastern portion of the county, whether derived from the Tertiary
sands or the chalk, is from one and the same source.
Near the outcrop of the chalk, the water is undoubtedly derived
from that portion of the rainfall which percolates into the chalk or
passes in through fissures from the superficial sands. Is the water in
the deeper portions, under central and east Essex, in part derived
from the sea, the character of the water being altered by the sands or
chalk through which it percolates? (The abundance of chlorides
and of magnesia salts would seem to indicate a much more direct
connection between the sea and the wells in several localities.)
Could slow filtration of the sea water, through such strata as we find
beneath the clay, remove certain salts from the sea water and at the
same time by some chemical action give rise to the formation of the
carbonate of sodium found in these waters ? If so, these saline
waters would naturally be found at the lower levels, whilst the
water percolating into the chalk near its outcrop, being less dense,
would, as it were, float upon it, and the line of demarcation might be
defined by the examination of waters from various depths and from
various parts towards the south, west, and north of the county.
The discussion of the relative values of these deep well waters
for domestic purposes is beyond the scope of the present paper; but
is one to which I am devoting some attention.
I had not intended publishing my analyses, or a paper on this
subject, until many more samples of water had been examined; but I
have had so much difficulty in obtaining samples from well authenti-
cated sources, and have been so perplexed with the variations found,
that I decided to communicate to the Field Club the results already
obtained in order to elicit criticism and opinions, and, if possible, to
obtain the aid of its members in conducting further researches,
which can scarcely fail to yield results of an interesting character.