UPPER TERRACE. 55 



Lea appear to be almost entirely Middle and Lower Terrace, 

 within our area, but east of that river there are wide spreads of 

 Upper Terrace gravel ; the first forms the highest ground at 

 Wanstead, and falls from 120 ft. in the north to 90 ft. in the 

 south; this patch must be regarded as Thames gravel, since a 

 deposit of the Lea in that locality would fall from east to west. 

 Beyond the Roding, a great area of gravel of this terrace is found 

 round Barking Side, and small patches continue through Romford, 

 Hornchurch (p. 46) and Upminster ; some of the gravels north 

 of West Thurrock may also belong to this terrace. 



On the south side of the Thames the large spread of Upper 

 Terrace gravel on Walton Common appears to belong jointly to 

 the Wey and Mole; corresponding gravels belonging exclusively 

 to the Wey occur in the neighbourhood of Addlestone and 

 Woodham. Owing to the southern encroachment of the Thames 

 between Windsor and Richmond (p. 63) it is only east of the 

 latter locality that we find the Upper Terrace of the Thames ; 

 little outliers may be noticed on the northern margin of Richmond 

 Park and north of Roehampton. The valley of the Wandle cuts 

 through the line, which is continued past Wandsworth and 

 Clapham Commons, the gravels of which may be referred partly 

 to the Wandle and partly to the main stream ; further south the 

 gravel extending from East Croydon to Thornton Heath belongs 

 to the Upper Terrace of the Wandle. 



Traces of Upper Terrace gravel have been detected south of 

 Camberwell and in Lewisharn, but no large expanse is found till 

 we reach the Dartford area ; Dartford Heath is formed by this 

 deposit, which attains the great thickness of 50ft., the base-level 

 being about 88 ft. above Ordnance datum ; this gravel contains 

 many ' foreign ' rocks derived from the Boulder Clay, including 

 the peculiar Rhaxella chert from the Corallian formation. 1 It 

 has been described fully by Messrs. Chandler and Leach, whose 

 papers will be further referred to when we come to deal with the 

 flint implements. 2 



The gravel of Dartford Brent was no doubt continuous with 

 that of the Heath, but is now separated from it by the valley of 

 the Darent. Important sections in the Horns Cross gravel have 

 been described by Mr. S. Priest, 3 and on the extreme eastern 

 margin of the map is a part of the Swanscombe deposit, famous 

 both for the fossils already alluded to and for the implements to 

 be discussed below. 



It will be seen from the above that, as Mr. T. I. Pocock 

 pointed out, the fall seawards of these gravels is, for the main 

 valley, practically negligible throughout our area, not exceeding 

 15 ft. in a distance of 37 miles. The deposits are usually, where 



1 A siliceous rock having the appearance of a fine-grained oolite, in which 

 the minute structure of the sponge Rhaxella can be recognised. Newton, E. T., 

 Proc. Oeol. Assoc., vol. xx, 1907, p. 127. 



2 See especially Proc. Oeol. Assoc., vol. xxiii, 1912, p. 102, and vol. xxiv, 

 1913, pp. 337-344. 



3 Proc. Geol. Assoc., vol. xxvi, 1915, pp. 78-85. 



