Changes in Geography and Climate. 39 
events during this somewhat obscure period. The unmis- 
takably Preglacial records cease, as already observed, with 
the temperate Cromer Forest-bed. Then succeeds a marine 
stratum showing a submergence of perhaps fifty feet, 
which cannot greatly have altered the outline of the 
country, though at present little is known about this epoch. 
Next follows a colder period, with Arctic plants ; and as 
these occur just above the present sea-level, and lie evenly 
on the strata below without deeply channelling them, the 
height of the land at the commencement of the Glacial 
Epoch, in Norfolk at any rate must have been almost the 
same as it is now. 
The freezing of the shallow land-locked North Sea, and 
the steady accumulation of snow, which could neither 
escape nor melt sufficiently fast, seems next to have 
resulted in the formation of an ice-sheet continuous with 
that pouring down from Norway and the Baltic, and this 
ice-sheet overspread the east of Britain as far south as the 
Thames. Whether the Arctic flora had sufficient time 
thoroughly to occupy Britain before this mantle over- 
whelmed the lowlands seems somewhat doubtful, for the 
only routes the plants could follow were across the North 
Sea, or the more southerly land-passage by the isthmus 
through which the Strait of Dover has now cut. The 
‘absence of any comparatively large-seeded northern plants, 
such as the Larch, Scandinavian Alder, or Arctic Poppy, 
either in a recent or in a fossil state, suggests that the 
small-seeded species that we do find were brought by 
birds, either across the sea or across the desert of ice, and 
did not come by land. To this epoch, when the drainage 
of a large part of Europe was poured into the North Sea, 
but could not escape northward on account of the ice, 
belongs probably the severance of England from the 
Continent, for the water was forced to cut itself a new 
