Ch. XIX] THE WEALD VALLEY WAS DENUDED. 285 



Lastly. The reader must recall to mind what was said in the 11th and 

 12th chapters, of the glacial drift and its far-transported materials. How 

 wide an extent of the British Isles appears to have heen under the sea 

 during some part or other of that epoch ! Most of the submerged areas 

 were afterwards converted into dry land, several hundred and in some 

 places more than a thousand feet high. It is an opinion very com- 

 monly entertained, that the central axis of the Weald was dry land when 

 the most characteristic northern drift originated ; no traces of northern 

 erratics having been met with farther south than Highgate, near London. 

 If such were the case, the Weald was probably dry land at the era when 

 the buried forest of Cromer in Norfolk (see above, pp. 136 and 153) 

 flourished, and when the elephant, rhinoceros, hippopotamus, extinct 

 beaver, and other mammals peopled that country. It may also be pre- 

 sumed that the Weald continued above the sea-level when that , forest 

 sank down to receive its covering of boulder-clay, gravel, chalk-rubble, 

 and other deposits, several hundred feet thick. But it by no means 

 follows that the area of the Weald was stationary during all this period. 

 Its surface may have been modified again and again during the Glacial 

 era, though it may never have been submerged beneath the sea. 



Mr. Trimmer has represented in a series of four maps his views as 

 to the successive changes which the physical geography of England and 

 parts of Europe may have undergone, after the commencement of the 

 Glacial epoch.* In the last but one of these he places the Weald under 

 water at a date long posterior to the forest of Cromer. In the fourth 

 map he represents the Weald as reconverted into land at a time when 

 England was united to the continent, and when the Thames was a 

 river of greater volume and of more easterly extension than it is now, 

 as proved by his own and Mr. Austen's observations on the ancient 

 alluvium of the Thames with its freshwater fossils at points very near 

 the sea. To discuss the various data on which such conclusions de- 

 pend, would lead me into too long a digression ; I merely allude to 

 them in this place to show that, while the researches of Mr. Prest- 

 wich establish the extreme remoteness of the period when the de- 

 nuding operations began, those of other geologists above cited, to 

 whom Mr. Martin, Professor Morris, and Sir R. Murchison should be 

 added, prove that important superficial changes have occurred at very 

 modern eras. 



In Denmark, especially in the Island of Moen, Mr. Puggaard has de- 

 monstrated that strata of chalk with flints, nearly as thick as the white 

 chalk of the Isle of Wight and Purbeck, have undergone disturbances 

 and contortions since the northern drift was formed.f The layers of 

 chalk-flint exposed in lofty sea-cliffs are often vertical and curved, and 

 the sands and clays of the overlying drift follow the bendings and foldings 

 of the older beds, and have evidently suffered the same derangement. 

 If, therefore, we find it necessary, in order to explain the position 



* Geol. Quart. Journ. voL ix. pi. 13. 



\ Puggaard, Moens Geologie, 8vo. : Copenhagen, 1851. 



