Geology and Physiography 17 



A few rolled Early and Middle Acheulean bifaces and Early Clactonian 

 flakes have been found in the warm gravels; while in situ at the top and 

 on the surface, there is a series of Middle Clactonian industries. In the 

 brown loams, a Middle to Upper Acheulean industry occurs in many 

 localities. 



The brown loam is capped with outwash gravels heralding the onset of 

 the Upper Chalky Boulder Clay ice sheet which advanced along the valleys, 

 partially enveloping the hill slopes and penetrating almost to the London 

 Basin at Hertford. This Boulder Clay is distinct from the earlier deposit 

 in its brown colour, due to the included brown interglacial loam and to 

 the large quantity of Bunter erratics. The earlier glacial and interglacial 

 deposits are folded and overthrust. There were two advances of the ice 

 and, during the intra-glacial period, some sands and loess-loams were 

 deposited in isolated pools on the surface of the Boulder Clay of the first 

 advance; there is an exposure at West Stow (Suffolk). It is probable that 

 the High Lodge Late Clactonian industry belongs to this period, because, 

 along with earlier forms, tools of that age appear in the gravels of Warren 

 Hill which is an outwash deposit formed during a halt in the retreat of the 

 ice sheet. Decalcification of Chalky Boulder Clay has given rise to a great 

 part of the sands of the Breckland. 



The three terraces of the river gravels are composite, and are cut out of 

 the earliest interglacial gravels and Upper ChaUcy Boulder Clay. After 

 the deposition of the latter, rapid erosion cut channels over 30 ft. deep. 

 Subsequent aggradation fdled these, and this gravel filling caps the Upper 

 Terrace. During the succeeding interglacial phase, 20 to 30 ft. channels 

 were cut and the Middle Terrace was formed of fine gravel carrying a 

 warm fauna and an industry with the very latest Clactonian technique 

 conjoined with LevaUois and Acheulean (St Neots; Milton Road, Cam- 

 bridge). A solifluxion layer on these gravels of the Upper and Middle 

 Terraces, and a deposit with a cold flora, indicate a third cold period 

 (Barnwell and Chesterton). The Lower Terrace is cut out of aU the 

 preceding deposits and is composed of fine gravel and silt with a poorly 

 marked solifluxion level in the gravel. 



THE POST-GLACIAL DEPOSITS OF FENLAND' 



The post-glacial deposits of the Fenland occupy a shallow basin centring 

 upon the Wash. They are of two types. On the landward side, they are 

 composed largely or wholly of peat, which has formed as a result of an 

 accumulation of fresh water augmented by the numerous large river 



' By H. Godwin, M.A., Ph.D. 



DBA 2 



