324 



This is proved by the remains of Mammoths found in 

 the peat-soil of Doggersbank. It is true that some believe 

 that sometimes the water temporarily covered thèse ré- 

 gions, e. g. in the first interglacial period, during which 

 the so-called Eem-Sea should hâve extended at least as far 

 as the présent isle of Goeree. But on the other hand the 

 Dutch soil must hâve been sloping to the south during 

 the ice-age, according to discoveries of northern stones 

 found far to the south, sothat the big rivers will probably 

 hâve had a more southern course. It is therefore quite 

 possible, that during the ice-age the Rhine took its course 

 through England. In addition to this the foUowing should 

 not be forgotten. If at the beginning of the ice-age the 

 Rhine flowed through England, it may be conceived that, 

 the ice-age having once properly begun, its further course 

 would hâve been towards the west, under compulsion 

 from the ice. It is therefore quite possible, that soon after 

 the ice-age this was the actual state of affairs. And such 

 plants, as were introduced eventually by the Rhine into 

 England, may be cxpected a priori somewhere to the 

 south-west of Cromer. 



Thf^ question, at what time river-plants had a last 

 chance to penetrate into England, is an important one. 

 This must hâve been the case in the so-called oak-period, 

 which is a fact of very great importance. With regard 

 to this a Word will hâve to be said about the periods, 

 which may be distinguished after the ice-age. There is in 

 the first place the so-called Dryas-period. The Tundra 

 gave way to a végétation of arctic-alpine dwarf-shrubs, 

 amongst which the well-known rosaceous species Dryas 

 octopetala L. with its eight white petals, différent species of 

 dwarf-willows, etc. This period brought us such plants as 

 the Empetrum nigrum L., the Arnica montana L. etc., which 

 hâve since continued to grow hère. The Dryas-period 

 was foUowed by a period of birches and Conifers, and 



