15 



III. The Blackwater Valley, Essex. 

 By W. H. Dalton, F.G.S., of H.M. Geological Survey. 



[Read March 26tli, 1881.] 

 Plate I. 



The lower part of the valley of the Blackwater offers some 

 marked peculiarities of geological, and therefore geographical, 

 structure, and it has occurred to me that a sketch of it might 

 form a useful illustration of ^ome general principles of those 

 sciences. 



From the range of the Chalk hills overlooking Koyston the 

 surface of the country slopes gently to the south-east as far 

 as Witham and Chelmsford, and then rises in the bold ridge 

 of Tiptree Heath and Danbury, separated by the estuary of 

 the Blackwater. 



Part of this area is drained northward by the Cam, which 

 has cut its way back through the escarpment of the Chalk 

 at Saffron Walden ; the western part is drained by the Lea, 

 and the north-east by the Stour and the Colne, whilst the 

 central part, extending from Dunmow to Coggeshall, may be 

 termed the Blackwater Basin, though the rivers traversing it 

 bear the names of Cann, Chelmer, Ter, and Guith, the 

 easternmost stream only being termed Blackwater. The 

 course of all these is, roughly speaking, south-eastward, down 

 the general slope, into which they cut more or less deeply. 

 On reaching the ridge mentioned above, they flow along its 

 foot from either end, successively combining with each 

 other, and passing into the estuary near the middle. I need 

 not enter into the subordinate deviations of these rivers from 

 their general course, but may remark, in passing, that the 

 upper part of the Blackwater proper, called the Pant, is in 

 the direct Hne of the Guith from Shalford to Bocking, and then 

 passes by a more easterly course to Coggeshall and Kelvedon. 



