HILL AND VALLEY DEPOSITS. 457 



admitted, and indeed seems incontestable, that after the date re- 

 ferred to the sea (or at least sea-water) once more covered the 

 greater part of the British Islands, hiding lands which now are 

 and previously had been eminent 1500 feet above the waves. The 

 evidence for this marine overflow, which was probably no sudden 

 catastrophe, but a gradual uprising of water, or subsiding of land, 

 is sufficient in the district now under review to a height of 750 

 feet, and may be conjecturally admitted for more ; but in Wales, 

 the north of England, and Scotland it is satisfactory to even twice 

 that height. The retreat of this water, or the subsidence of this 

 land, was also probably gradual, not sudden, occupied a long time, 

 and was attended by enormous local waste of surface. By both 

 operations, long rising and falling movements, abundance of dis- 

 integrated earthy and stony masses acquired a new distribution ; and 

 on the glacial waters, for they seem to have been cold and to have 

 nourished boreal mollusks, to areas once occupied by cognate races 

 adapted to warmer climates, some larger blocks were carried far from 

 their native sites in the Grampians and Lammermuirs,in Cumberland, 

 Yorkshire, and Wales, to the plains of Cheshire and Staffordshire. 



On this anciently upheaved and again deeply sunk sea bed, 

 subsequently restored to its old level, worn and wasted, and with 

 abundant marks of marine occupation, an entirely different set of 

 deposits, in a considerable degree characterized by levels, com- 

 position, and organic contents, as river and flood sediments, has 

 been collected in the course of the basin of the Thames. These 

 are thought to be of various ages, but all may be understood as 

 due to watery agency, principally fresh-water currents which 

 flowed while the general surface of the country was not materially 

 different in respect of elevation and contour from what it is at 

 present. For these I employ the general title of Valley deposits. 



But beside these gravels, sands, and clays, observed on the bed 

 and on the lower slopes of the Thames basin, we find, sometimes in 

 great quantity and often widely scattered over hills and dales, a 

 variety of gravels and sands, or else of clay charged with angular, 

 rolled, or rubbed stones, which have been brought from distant 

 parts of England, or even from beyond the Isles of Britain. To 

 these I assign the title of Hill deposits, not that they are exclu- 

 sively found on elevated ground, but because this fact is charac- 

 teristic of them, in contrast with the others. Scattered materials 



