ALLUVIUM. 75 



Scrobicularia plana Da Costa and Tellina (Macoma) balthica 

 Linne occur at Crossness and elsewhere lower down the valley. 1 

 It is doubtful whether any of the mollusca found in the 

 Holocene deposits are extinct at the present day ; Pisidium 

 supinum A. Schmidt and Planorbis strcemii West, long regarded 

 as such, have now been discovered living in Britain. 



The plant -remains found in deposits of neolithic age indicate 

 temperate conditions and include the alder, ash, beech, birch, 

 holly, ivy, maple, oak, pear, pine or Scotch fir, poplar, willow 

 and yew. 2 



The Alluvium in the Colne Valley consists of loam, shell- 

 marl, and gravel. By the Staines Reservoir remains of elk, 

 fallow deer and other animals were obtained, and identified by 

 Mr. E. T. Newton. 8 



In the Lea valley clay, loam, peat and shell-marl occur in 

 irregular beds, 12 ft. or more in thickness, with evidence of 

 local erosion and deposition, so that deposits of different ages 

 occur at the same level. At Ponder 's End Mr. Warren found 

 fragments of pottery and flint chips at the base of the Alluvium, 

 and considers that the deposit may be of early Bronze Age; 

 further up the river, at Chingford Reservoirs he records Romano- 

 British pottery. 4 The modern alluvial mud is well seen between 

 Blackwall and West Ham. 



Remains of beaver have been found in considerable numbers 

 at Walthamstow, as pointed out by Henry Woodward, who 

 expressed his opinion that the animal had been an important 

 geological agent in that region of the old Forest of Waltham. 

 Thus ' every stream is converted by the Beavers into a series 

 of falls with beaver -dams, and large, deep, clear, still pools of 

 water. It is evident that, if ever a big flood came down such 

 rivers, these beaver-dams would be quite calculated to cause 

 an overflow and an inundation of the Forest for miles around. 

 Many of the forest -trees could not stand this excessive damp, 

 and would give way to Sphagnum or bog -moss ; and large tracts 

 thus flooded would be converted into peaty, marshy fen -land.' 



The fallow deer has also been found in the Alluvial deposits 

 of Walthamstow. 



Many sections of Alluvium along the main valley have been 

 described, notably at North Woolwich, and Crossness, where 

 numerous plants were obtained, and remains of beaver and other 

 animals. 



At Beckton excavations for the Gas Works yielded neolithic 

 implements, mammals, including dolphin and a whale, and 

 mollusca ; a bed of peat, impersistent but sometimes as much 

 as 7 ft. thick, contained much wood, including bog-oak. 



1 Spurrell, F. C. J., Proc. Geol. Assoc., vol. xi, 1891, p. 214. 



2 Reid, C., ' Origin of British Flora,' 1899, pp. 55, 64, etc. 



3 ' Summary of Progress for 1902 ' (Mem. OeoL Surv.), 1903, p. 207. 



4 Quart. Journ. OeoL Soc., vol. Ixviii, 1912, p. 226; and Proc. Geol. Assoc., 

 vol. xxii, 1911, p. 170. 



