65 



NOTES ON THE GEOLOGY OF THE NEIGH- 

 BOURHOOD OF CHELMSFORD. 



P.y T. V. HOLMES, F.G.S. 

 \_Preparedfor t/te Mcethii; at Braciiificl.l an.i Cliclmsford, on April isth, rSg3.\ 



A T 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 

 patclies 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 



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