1867.] 



WOOD SOUTH-EAST OF EXOLAXD. 



415 



mouth and allied vaUeys to a period so recent as to be posterior to 

 aU gravel or brick-earth accumulations. It is impossible to make the 

 structure exliibited by this group of vaUeys intelligible without the 

 assistance of the map and sections given in the memoir ; but the fol- 

 lowing section at Maldon indicates that the Blackwater there occu- 

 pies a line of Postglacial dislocation, on the south of which an eleva- 

 tion accompanied by denudation has taken place, from which the 

 north side has escaped. 



Pig. 1.5. — Section across the valley of the BlacTcwater at Maldon. 



Line of dislocation and of the River. 

 1. London Clay. 2. Middle Glacial Gravel. 3. Upper Glacial Clay. 



This dislocation is so continuous along the estuary, that at its 

 eastern extremity, at Bradwell, the Postglacial or valley -formed East- 

 Essex gravel is at a level as high as, and even higher than, the Glacial 

 beds on the opposite side of the estuary; albeit that this gravel is coeval 

 with and intimately allied to that of the Thames, which, as I have 

 shown, rests in a trough cut down (in one part at least) to a depth 

 of 600 feet from the Glacial beds. Properly to apprehend this 

 anomalous position it is indispensable that the grouping of the beds 

 should be studied on the map. 



In concluding this partial epitome of the structure examined in the 

 manuscript memoir, I am anxious to call attention to two things : 

 one is that the Postglacial structure of the area examined appears 

 to me to be at variance with any general period of high- and low-level 

 gravels, the extensive disturbances prevailing during the Post- 

 glacial denudation having, according to my views, placed the gravels 

 at aU elevations quite irrespective of their age. The other is that, 

 if these views are weU founded, the valleys within the area thus 

 examined must have been whoUy formed since the Upper Glacial clay*. 

 Whatever may be the opinions of geologists as to the disputed beds 

 of Lenham and Paddlesworth, few, I apprehend, would deny that the 

 principal part of the denudation which has swept so much of the Ter- 

 tiary strata off the south of England, be the period of it when it may, 

 has been common also to the north of France. It is important there- 

 fore to ascertain what has been the point corresponding to the northern 

 brow of the Thames valley from which the denudation of Prance has 

 descended. Some time since f, I called attention to an identity which 



* One or two exceptions only exist to this general proposition, and where 

 preglacial depressions are recognizable as existing valleys. One of these is the 

 long dry valley through which the railway runs from Welwyn to Hitchin. 



t Ann. and Mag. of Nat. Hist., 1864, 3rd .ser. vol. xiii. p. 185 ef seqq. 



