60 



Wood-^ Structure of the Thames Valley. 



its normal thickness of 12 to 15 feet at Hford 

 Station, a distance of only half a mile. East- 

 wards from the Station, and but half a mile 

 further, the lower brickearth again comes up 

 from under the gravel at the London Eoad field 

 where the gravel is almost wholly denuded 

 from it. This brickearth has a very limited 

 development, but may everywhere be distin- 

 guished from the upper brickearth by its rest- 

 ing direct upon either the London clay or the 

 lower tertiary sands, and by its position rela- 

 tively to the Thames gravel. It occurs in the 

 pits near Erith; where it has a thickness of 

 about 30 feet,^ resting on Lower London Tertiary 

 sand, and is almost horizontal, but it passes 

 northwards towards the river and beyond the 

 pits imder the gravel. It occurs also in Wick- 

 ham Lane Brickfield (see Section No. 2), where 

 a thickness of 15 feet of the deposit is exposed 

 thrown into an inclined position, the dip being 

 very marked and amounting to 18°. With the 

 exception of small patches on the tops of the 

 hills west of Wickham Lane, which the denuda- 

 tion accompanying the violent break-up in that 

 direction has spared, these are the only expo- 

 sures of the lower and oldest brickearth. The 

 deposit seems to have been very limited, but 

 it is that which has furnished the chief part of 

 the Mammalian remains that enrich several pri- 

 vate as well as the National collections. 



2. The Thames Gravel (xA:"). — Next in suc- 

 cession comes the great sheet of gravel which, 

 wherever not denuded, consists of a persistent 

 well-marked deposit, reaching occasionally to a 

 thickness of 20 feet, but usually from 12 to 15 ; 

 spreading over and far beyond the lower brick- 

 earth, and up the north side of the valley to a 

 height of more than 100 feet above it. There 

 seems no reason for regarding this gravel as 



iH'i other than marine ; but at a few places near its 

 C.3 o f edge, as at Brentford and West Hackney,^ fresh- 

 5\° 1 1 water shells have been found in a band of sandy 

 g^JcS clay, either intercalated in the gravel or under- 

 .§1^:;, lying it. Mammalian remains, too, have been 

 "^lla found in a few places in it, a feature common 

 loia also to the marine sands and gravels of the 

 ^^^Z Middle-drift. 



3. The Upper Brickearth {x^'").—Thxs, is the 

 brickearth which has so large a spread in the 



A thin band of shingly grarel occurs in it towards the upper part. 



Morris, Quart. Journ. Geol. Soc, vol. vi., p. 201. Prestwich, ib., vol. xi., p. 107. 



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