Wood — Structure of the Thames Yalley. 



5. Tlie Forest and Peat (y). — For a few miles 

 •3 J I fg 03^ ii^Q ga^g^ gi,jg Qf London, we find a bed of 



J peat, containing the stems of trees,' and resting 

 H on tlie gravel (x 4z") or else upon the upper 

 t. brickearth {x4l"). When this formation was 

 3 . cut through in forming the sewer through the 

 ^=3 Plumstead Marshes, stools of trees were ex- 

 ^" posed at the base of the peat, rooted into the 

 \ ** gravel at a depth of some 20 feet below the 

 I . surface of the marsh (see y in section 3). This 

 : I peat is overlain by the marsh-clay (z) formed 

 t^ by the river-mud before the stream was em- 

 l^ banked. 



l^ In the formations before described we have 

 (7,^1 I ;;; ^ thc followlug succcssion of events subsequent 

 {■S r Ih B-i ^'^ t^6 conmlete formation of the original valley 

 ' g by denucfetion through the Boulder-clay or 

 3 m Upper-drift — First, the deposit of the lower 

 d| brickearth (a; 4') ; Secondly, the deposit of the 

 :h Thames gravel (a; 4''') ; and Thirdly, the deposit 

 ;^ of the upper brickearth (a;4'''). These are the 

 I deposits of the original valley. Then comes 

 r^ the upheaval of portions of the original valley, 

 !■§ the dislocation of its deposits, and the exten- 

 i-l sive denudation of the uppermost of them 

 U (33 4''''') ; with the more partial denudation of 

 ; g, the intermediate deposit, the gravel (x 4/') ; 

 iP while of the lower (a; H) a portion was detached 

 ;? that eventually has become isolated by a fault 

 ^ behind the Chalk cliff, capped with Lower Ter- 

 I . tiary sand and pebble, which forms the south- 

 1 J west side of Bostol Hill, in Kent, as shown in 

 '§ section 3. By the same upheaval and denuda- 

 1% tion we have the southern slope of the original 

 l-g valley east of London destroyed, with the ex- 

 pi ception of a remnant forming Shooters Hill, 

 iS and in its place the formation of the subsidiary 

 « valley of the Cray, and of that in which we 

 ; 3 find the Grays deposit resting ; both being cut 

 ; I through the Thames gravel («4'') and subjacent 

 ; ° Thanet sand down to and into the Chalk itself. 

 'f^ Then we have the accumulation in one of these 

 I ^ of a fluviatile deposit {x 6') some 40 feet thick, 

 ;:§ underlain by another gravel (xo) which we 

 P^' also find resting on the Chalk in several places 

 '."f in the Cray valley. 



'<5 Further we find the gravel (a;4''') and the 

 ."*' upper brickearth (a; 4''^'') where not denuded, 

 i forming after this upheaval a land surface, and 

 I supporting a growth of forest ; that surface then 



^ Mostly of yew, but oak and pine occasionally occur. 



*!8 !* a 



