HARMER : THE PLEISTOCENE DEPOSITS OF EAST AXGLIA. 323 
With these recent and boreal shells, the kind of fauna one 
might expect to meet with in an East Anglian bed of Glacial 
age, Wood and 1 found, however, a few specimens, most of 
them small and some very fragile, of southern and extinct species 
which had been common in the North Sea during earlier and 
middle Crag times, but had died out there, as far as we know, 
long before the Pleistocene period. To explain this anomaly 
it has been suggested that such forms had been derived from 
some older Crag deposits. Xo evidence has ever been offered 
for this view, however, and I have elsewhere given the reasons 
why I am unable to accept it.* 
If, as before urged, the area now under discussion was 
occupied during the deposition of the Contorted Drift of Cromer 
and the country to the south of it by a basin, from which tidal 
currents were excluded, closed to the north by ice and to the 
south by the land barrier which came into existence early in 
the Red Crag period, beds of laminated, or quasi-stratified 
brickearth might accumulate in it, but it is difficult to see how 
a great sheet of false-bedded sand and gravel, such as that of 
the Middle Glacial of the eastern part of Norfolk and Suffolk, 
which, moreover, seems to be of marine origin, could have done 
so.f The Middle Glacial sands, though intercalated between 
deposits of a highly glacial character, give no indication of the 
existence of ice, either floating or otherwise, in the area just 
named at this period. J 
If, as already suggested, a breach in the south-western 
boundary of the supposed extra-glacial lake was at this time 
opened, and tidal currents from the south were reintroduced, the 
latter might have brought with them a few specimens of some 
small and fragile mollusca, which had till then hngered on in 
the English Channel, though they had long ceased to inhabit the 
North Sea. A similar difference now exists between the molluscan 
fauna of the eastern and southern coasts of England, which are 
* Loc. cit., p. 461. 
t Further to the south-west the gravel and sand of the Middle Glacial 
were, no doubt, due to streams issuing from the inland ice. 
J In the western part of the East Anglian area covered by it, however, 
the Chalky Boulder-clay is, in places, interstratified with sand or gravel. 
