Wood — Structure of Valleys in Essex. 349 



in its constituent material and thickness, intimately resembles tlie 

 Thames gravel. It also presents a complete parallel to that gravel, 

 in being capped in parts with a brickearth, into which it passes up- 

 wards through bands of " race," or gravelly brickearth. This brick- 

 earth is usually from 5 to 8 feet in thickness, but, at Hoo, near 

 Eochester, it attains the thickness of 35 feet, which, as the deposit 

 has everywhere been more or less denuded, may not be exceptional, 

 but may, perhaps, rejDresent its original depth as deposited. Like 

 the Upper Brickearth [x^'") of the Thames Valley, it is evidently a 

 continuation of the gravel deposit, by a cessation of the sea-borne 

 gravel material, and by the precipitation of the river-supplied mud 

 in lieu of it. The denudation removing it has operated chiefly 

 between Hoo and the Nore, and again, from a few miles north of 

 Southend, as far as the northernmost extremity of the deposit. The 

 delineation of the gravel in the Map accompanying this paper renders 

 any description of its area unnecessary ; but I should observe that, while 

 the continuity of the gravel-sheet in its course from Eochester to 

 Bradfield on the south of the Blackwater Estuary (interrupted only 

 where the mouths of the Thames and Crouch cut it at right angles), 

 as well as the uniformity throughout of its constituent material, 

 affords satisfactory evidence of its identity, there is not the same 

 conclusive evidence of its occurrence on the north side of the Black- 

 water estuary. A small fault in one of the Bradfield pits, which 

 has let down some six feet of the Brickearth beside the gravel, and 

 which shows also the passage upwards through " race," identifies the 

 gravel immediately opposite the western extremity of Mersey Island 

 as that of the East Essex sheet ; while a temporary pit, some 20 

 feet deep, made on this extremity of Mersey Island, satisfied me 

 (against a previous impression to the contrary) that the sand, with 

 occasional gravel bands of that island, is not any part of the East 

 Essex gravel, but belongs to the great deposit of the Middle Drift, 

 which adjoins it on the north-east. On the other hand, the occurrence, 

 in profusion, in the gravel which forms Clacton Cliff, of those frag- 

 ments of minutely pitted sandstone so characteristic of the East 

 Essex gravel in its undoubted districts, and which do not occur in 

 the gravels of the Middle Drift, when coupled with the complete 

 detachment of the Clacton Cliff gravel from the great and continuous 

 tract of Middle Drift, would seem to identify that gravel with the 

 East Essex deposit ; but this identity is rendered more certain by the 

 occurrence of a patch of the Upper Brickearth at one part of the cliff.^ 

 Associated with this gravel at Clacton occurs a very rich fluviatile 

 and fluvio-marine deposit, which has been long known. Their rela- 

 tive positions will appear by Section 8. (See margin of Map.) It 

 will be seen that the fluviatile and fluvio-marine deposit {x 5) has 



^ This patch is of limited extent, and occurs about 1500 yards south-west of Tower 

 Hill and 500 of Holland Gap (its longitudinal dimensions are unavoidably ex- 

 aggerated in section 8). About a mile and a half from the north-eastern termination 

 of section 8, small patches of the Middle Drift sand occur on the summit of the much 

 loftier (London clay) Cliff of Frinton. The patches are but a few feet deep, and are 

 best exposed under Frinton Old Church, and their distinctive character from the 

 Clacton gravel is very apparent. 



