MINERAL WATERS AND MEDICINAL SPRINGS OF ESSEX. 213
but is not in any way disagreeable, and is used regularly for
domestic purposes by the occupants of an adjacent cottage. A
sample obtained in July 1907 yielded the following results:—
This is apparently an ordinary Boulder-clay water. The
fact that this clay contains much chalk accounts for the large
amount of calcium carbonate present. The Boulder-clay is not
far away, and probably a strip or outlier of it extends to the
vicinity of the well. In any case, this water resembles others
from the Boulder-clay. There is just enough iron to give the
water a marked chalybeate taste, but not enough to give it any
medicinal value.
Mr. Dalton writes, however, that :—" The site of this spring
is mapped as London Clay, some distance below the Glacial
Gravel, and beyond reach of any infiltration of drainage from
the Boulder-clay. It may obtain its carbonate of lime from the
London Clay Septaria."
(7.)—The Mark's Hall Spring.—Another small and unimportant
spring, discovered and first recorded in 1699 by Allen,66 lay
somewhere in the parish of Mark's Hall, some six miles and a
half east-north-east from Braintree. He classes it as a "Chaly-
beat-water containing a nitrous salt," and says:—
" This water, joyning another, incrusts, as do the rest. It is much the same
with the preceding [i.e. Knaresborough], containing little steel, but a large share
of an acid, not so fugitive as where it is in less quantity or ill-coupled. With a
salt, it gave a bright red, a very little purplish, not so deep as the preceding.
The colour it advanced with gall, it lost again two days after, without precipita-
tion of any ferrugineous parts, in which it differs from other chalybeats. It
rendered a solution of sal saturni troubled, but not very milky; much as the rest ;
and it tinctur'd a high yellow with Lignum Nephriticum, as do nitres, and a
little clouded. It weighed, likewise, as the other, just the weight of common
water."
66 Chalybeat and Purging Waters, p. 21 (1699). It appears not to be noticed in Allen's
second edition (1711).