65
NOTES ON THE GEOLOGY OF THE NEIGH-
BOURHOOD OF CHELMSFORD.
By T. V. HOLMES, F.G.S.
[Prepared for the Meeting at Broomfield and Chelmsford, on April 15th, 1893.]
AT Chelmsford we are in the middle of a district in which the
London Clay is the oldest formation anywhere visible. South-
ward this area includes the whole of Essex, with the exception of
the small tract between Rainham and Stanford-le-hope; northward,
its boundary is a nearly straight line connecting Bishop Stortford
with Sudbury and Ipswich. Looking at Chelmsford as a centre from
which to make geological excursions, we find it well-suited to that
purpose. If we walk or drive ten or twelve miles in a southerly
direction, we are in a district of London Clay, which at one spot
may form the surface for a few square miles, while at another it
appears only in the intervals between overlying beds of the Bagshot
Series or patches of Boulder Clay. There are, besides, many isolated
patches of gravel, some probably older, some later in date than the
Boulder Clay. Thus in southern Essex, in spite of the uniform
softness of the rocks composing its geological structure, there is a
considerable variety as regards height and contour of the surface.
But if we travel north of Chelmsford, towards and beyond Broom-
field for instance, we find ourselves in a region in which the varied
contours of the south are altogether wanting. We see that the
country consists of a remarkably flat-topped plateau, intersected
here and there by the valley of some stream, which is as uniform in
aspect as in composition. We are, in short, entering the district
occupied by the broad expanse of the Chalky Boulder Clay, a forma-
tion which gives so strong an impression of monotonous flatness to
the traveller through northern Essex, Suffolk, and Norfolk. This
monotony of the landscape north of Chelmsford and its comparative
variety southward are simply the result of geological structure. About
Broomfield the plateau is everywhere capped by Boulder Clay, the
underlying sand and gravel associated with it becoming visible in the
sides of the river-valleys intersecting the plateau, while below the
sand and gravel London Clay occasionally appears. This sand and
gravel is well shown in the pit near the new water-tower at Rainsford