14 THE \OX-MARINi: MOLLl'SCA OF THE RIVER LEA 



Tliames, which is generally considered to represent a late 

 stage of the Pleistocene. The section here given (Fig. i) may 

 be taken as a typical one. Here the division of the upper bed 

 into loamy-clay and peat is well shewn. 



In our opinion the peat represents the deposit accumulated 

 in the valley before any reclamation had taken place, whilst the 

 loamy clay has been deposited by flood- water since man had 

 altered the original condition by embankments and other works. 

 Knowing only too well by past experience the difficulties 

 arising from the shifting of the course of a stream, our work was 

 principally confined to the parts away from the influence of the 

 main stream. It should, however, be borne in mind that the 

 modern deposits of the River Lea, caused by erosion and 

 subsequent deposition, difl'ered lithologically from the older beds, 

 for the former in all cases consisted of sand or sandy gravel with 

 but little vegetable remains, so that tliere was never any difficulty 

 in dealing with such cases. It must also be noted that when a 

 stream washes aw^ay an old deposit, many of the shells, though 

 apparently fragile, will be drifted down and safely deposited 

 elsewhere, so that the new bed would contain the shells living 

 at the time of deposition mixed with those derived from older 

 beds. That the age of some patches of the shell marl dates 

 back to Neolithic times is evident from the discovery of 

 Neolithic flakes in situ under such conditions that they can only 

 have been dropped where now found from the hand of man. In 

 1897^, ^^'^ gave to the Essex Field Club an account of the 

 Mollusca from these beds, yet the new facts accumulated are of 

 so much importance as to justify the production of this 

 -additional paper. 



MOLLUSCA OF THE MODERN DEPOSITS. 

 The following species were obtained from the loamy-clay : — 



Vitvea iiitidula (Drap.) LiuuKva pevegev (Miill.) 



Hygromia hispida (Linn.) ,, tynncatula (Miill.) 



Vallonia piilchella (Mull.) Planovhis mafginatus, Drap. 



Helicigona avbustorum CLinn.) ,, vortex (I^inn.) 



Helix nemoralis, Linn. ,, spirorbis, Miill. 



Cochlicopa lithvica (Miill.) Bithynia tentacidata, Linn. 



Pupa mnscorum (Linn.) „ leachii (SJiepp.) 

 Sncccinea elegans, Risso. 



2 Kknnari) a. S., and Woodwak-p, B. B. The Post-Pliocene N'on-marine Mollusca o 

 Ebsex. Ivssr.x Xat., vol. x., i)p. S7 — loy. 



