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 



