Wood— Structure of the Thames Y alley. 



Gl 



Thames Valley, and rests on the gravel. 

 Consisting of a tawny loam, it is much in- 2 i 

 ferior in thickness to the lower brickearth, f ■; 

 being usually from 5 to 8 feet in thickness, -g ^ 

 and it has not furnished that rich series of '^•- 

 fossils which has been obtained from the 

 lower. It appears, however, to be every- -^ 

 where conformable to the gravel, but does --> % 

 not generally reach so far up the valley as ^ 

 the more outlying portion of the gravel. ^ 

 Its chief development is in the east near ^- 

 Wanstead and Tottenham, and in the west Vo 

 around West Drayton ; but it has a gre^t ^ 

 extent in many places between both ex- "^ 

 tremities of the valley. The next Section, ^ "g 

 No. 3, exhibits the relation of the lower =S I 

 brickearth to the gravel and the %pper -g b 

 brickearth, and the dislocation by which pq ^ 

 the lower has been brought into its in- g 

 clined position at Wickham. i^ 



4. The Grays Brickearth {x5'). — The S 

 Grays deposit is distinct from all those -^ 

 described. It consists of 15 feet of blue g .| 

 clay, containing Cyrena fluminalis and other ^ "S 

 pure freshwater shells, overlain by 20 feet '5 ^ 

 of sand which in places is false-bedded. * 

 The clay is underlain by a few feet of '3 

 flint-gravel coarser and more angular than ^ 

 the Thames gravel (x^"), and that again •§ 

 by redeposited Chalk, termed by the work- „ 

 men " Bullhead." Section 4 shows the ^ 

 deposit, as exposed by the three pits, and ^ 

 its relation to the Thames gravel and upper J 

 brickearth. Here we see that the upthrow | 

 and denudation which succeeded the deposit ^ 

 of the upper brickearth, and preceded the S s 

 Grays deposit, has along the line of section ^ % 

 removed all but a fragment of the upper I ^\ 

 brickearth, and has in one place removed '? .9, 

 the gravel (xi/') and the subjacent Thanet S I, 

 sand (h) , exposing the Chalk ; while at one g p-- 

 extremity of the section a newer, and sub- "^ 

 sidiary, valley in which the Grays deposit 

 (x 6') rests, has been formed by the cutting 

 down of the Thames gravel and Thanet 

 sand to the Chalk, as well as of the Chalk ^ « 

 itself. In all respects the position of this « g , 

 subsidiary valley coiTCsponds to that of il^E 

 the valley of the Cray cut through Dart- « g "* ^ 



ford Heath, while the gravel at the base of the Grays deposit corres- 

 ponds with the gravels of the Cray valley. 



