" FRESH - WATER CHALK " AT HALSTEAD,
ESSEX.
By T. S. DYMOND, F.I.C, and F. W. MARYON.
[Read December 11th, 1897.]
ON the slope of a little valley at Mr. C. W. Gray's farm,
"Perces," Greenstead Green, Halstead, there is a very
singular deposit of chalk-like material. It occurs at a depth of
from 6 to 8 inches below the surface, and it is covered by soil
blackened by humus. A spring of water renders the land very
wet, and to this is due the accumulation of humus in the soil,
the natural decay and oxidation of vegetable matter having been
arrested. At the spot examined, the deposit was at least three
feet thick, and may have been much more. As is seen by the
Drift Map (Sheet 47), the subsoil in this locality is chiefly
Boulder-clay, but in the valleys there is an outcrop of gravel
with London-clay underneath, and it is on one of these that
this chalk appears to be resting. No similar deposit has, as
far as we know, been recorded in this locality, and it therefore
seemed worth while to examine it more closely.
The chalk is soft and granular in character. Examined
under the microscope it appears as a white amorphous substance
mixed with small transparent particles and devoid of the
remains of any organisms. The transparent masses are un-
doubtedly crystalline, but it is not possible to identify the
crystalline forms with either calc-spar or aragonite. Dried at
100°C and submitted to analysis it was found to have the follow-
ing percentage composition :—
That this is a comparatively recent deposit we think there
can be no doubt, for it lies above the London-clay and either in