THE DISTRICT AROUND CHELMSFORD.
175
change of current, rocks were brought here from a slightly different
source. Much more information is, however, required before any
definite conclusion can be arrived at.
The yellow clay at the top remains the same, and still maintains
its reputation of being one of the best soils, when well treated, for
growing wheat and barley, especially the latter. Although not
naturally fertile, it well repays liberal treatment, and the quality of
the corn, especially of barley, grown on this soil compares favourably
with that of any other in England.
The characteristic outline of this district is that of gently undulat-
ing hills, varying from 120 to 200 feet, and more, above the level of
the sea, and divided by small brooks which have worn themselves
wide shallow valleys, and have formed here and there (probably in
times of flood) large alluvial beds containing remains of many shells,
some of them being species not now found in the district.
One shell in particular, viz., Cyclostoma elegans, is very abundant
in some of these deposits, and is found nowhere else in the neigh-
bourhood, or, so far as is known, nearer than the chalk hills round
Linton, Cambridgeshire, a distance of thirty miles, roughly speaking.
As none of our present river valleys extend so far in that direction,
the shells could not have been brought here from Cambridgeshire,
but must have existed on our hills of Boulder Clay at the time the
alluvium was deposited.1 I should imagine that cultivation has had
a good deal to do with its extermination, there being no grassy hills
or sheep-fed upland pastures on which the mollusc could live.
In January, 1888, I had an opportunity of examining a section of
one of these alluvial deposits at "Duke's Farm," Roxwell, which the
owner was draining. It is situated about ten feet above the level of
the present stream. The first two or three feet consisted of a
dark peaty soil, formed almost entirely of decayed vegetable
matter, and containing many shells. Under this was a stratum of
whitish clay from four to six feet thick, almost devoid of shells, and
below was probably the London Clay, but it was impossible to
bottom it on account of the water.
The shells collected from this deposit were named for me by Mr.
1 I may mention here that one living specimen of C. elegans is reported to have been found at
Pleshey by Miss E. L. Christy several years ago, the authenticity of which I have no reason to
doubt; but Mr. Miller Christy, who has collected shells in this district for many years, has never
found it. The fact that Pleshey Mount is the only locality from which Cyclostoma is reported
seems to be in favour of the view of its comparatively recent extermination by agricultural
agencies ; Pleshey being an artificial mound of Chalky Boulder Clay covered with short grass,
undisturbed by the plough, renders it a very good imitation of the chalk downs preferred by the
mollusc.