CHAP. xir. AND HOXNE DEPOSITS. 227 



In the interval we must suppose repeated oscillations of level, 

 during which land covered with trees, an estuary with its 

 freshwater shells, and the sea with its Mya truncata and 

 other mollusca still retaining their erect position, gained by 

 turns the ascendency. These changes were accompanied by 

 some denudation followed by a grand submergence of several 

 hundred feet, probably brought about slowly, and when 

 floating ice aided in transporting erratic blocks from great 

 distances. The glacial till, No. 4, then originated, and the 

 gravel and sands, No. 5, were afterwards superimposed on 

 the boulder clay, first in horizontal beds, which became sub 

 sequently contorted. These were covered in their turn by 

 other layers of gravel and sand, No. 6, pp. 213 and 224, the 

 downward movement still continuing. 



The entire thickness of the beds above the chalk at some 

 points near the coast, and the height at which they now are 

 raised, are such as to show that the subsidence of the country 

 after the growth of the forest bed, exceeded four hundred feet. 

 The re-elevation must have amounted to nearly as many feet, 

 as the site of the ancient forest, originally subaerial, has been 

 brought up again to within a few feet of high-water mark. 

 Lastly, after all these events, and probably during the final 

 process of emergence, the valley was scooped out in which 

 the newer freshwater strata of Mundesley, fig. 33, p. 224, were 

 gradually deposited. 



Throughout the whole of this succession of geographical 

 changes, the flora and invertebrate fauna of Europe appear 

 to have undergone no important revolution in their specific 

 characters. The plants of the forest bed belonged already to 

 what has been called the Germanic flora. The mollusca, the 

 insects, and even some of the mammalia, such as the European 

 beaver and roebuck, were the same as those now coexisting 

 with man. Yet the oldest memorials of our species at present 

 discovered in Great Britain are post-glacial, or posterior in date 



Q 2 



