DAWN OF THE MODERN FLORA _ 165 
at length made their appearance—Marsh Marigold 
(Caltha palustris), Sloe (Prunus spinosa), Blackberry 
(Rubus fruticosus), Hawthorn (Crategus Oxyacan- 
tha), Cow Parsnep (Heracleum Sphondylium), Bog- 
bean (Menyanthes trifoliata), Gypsywort (Lycopus 
europeus), Sheep’s Sorrel (Rumex Acetosella), Birch 
(Betulaalba), Hazel (Corylus Avellana), Oak (Quercus 
Robur), Yew (Taxus baccata), Bur-reed (Sparganium 
erectum), Cotton-grass (Eriophorum polystachion), 
Royal Fern (Osmunda regalis). The remains of 
these occur in the “Cromer Forest-bed,” a series of 
estuarine deposits—laid down perhaps by the ancient 
Rhine—which underlies the boulder-clay cliffs of the 
Norfolk coast, and forms almost the only plant-bear- 
ing beds of Pliocene Age found in the present land 
area which we call Britain. 
And now, just as a point is reached when at length 
we think we shall see our present British flora emerg- 
ing fully from the obscurity of the ages, a dramatic 
interruption occurs, which confuses the record and 
brings us into difficulties of many sorts, giving rise to 
controversies which are still far from being settled. 
The climate becomes suddenly colder, and Europe is 
plunged into the rigours of the Ice Age. Ice Ages 
there had been before in the long history of the world. 
Rocks of late Permian or early Carboniferous times 
bear ample witness to the existence of great ice sheets 
extending over wide areas in several continents where 
temperate or warm conditions now prevail: and 
puzzling deposits of later age—Cretaceous, Eocene, 
Miocene—have been interpreted by some geologists 
as the relics of subsequent Glacial Periods. But 
these are only distant echoes as compared with the 
