PLIOCEE-E PERIOD IN" ENGLAKD. 483 



sion thus increasing southwards and westwards on the eastern, and 

 northwards and westwards on the western side of England, the ice 

 at the close of the Chalky Clay entered the sea, which at this time 

 covered the Thames and Severn systems, and was still sufficiently 

 deep to submerge some of the water-partings between the Thames 

 and Severn, and that also between the Severn and the Welland, in 

 the following way. It entered the sea over the Thames system by 

 the valleys of the Eoding and Lea in Sheet 1, by that of the Colne 

 in Sheet 7, and over the water-parting, probably then emerged, 

 between the Ouse and Thames systems in Sheet 46, overwhelming, 

 as it did so, a small island represented by Stewkley and the country 

 a short distance around that village, and another represented by 

 Whaddon Chase ; while in Sheet 53 it entered the Severn system 

 by the valley of the Wariuickshire Avon, which is a branch of the 

 Severn. The extent to which the water-partings had at this time 

 emerged I shall examine in Stage Y. 



Thus we find the partially emerged condition of England at the 

 close of the Chalky Clay ; and it is easy to carry back from it our 

 ideas to that more submerged condition when the laying down of 

 this clay commenced, and when ice, which had been in existence 

 during the formation of the Lower Glacial beds h2 and h S (and, as 

 shown in describing Stage I., even during the Crag, though it may 

 not have reached the sea), after retreating in consequence, even in 

 the east, partly of increasing submergence, but mainly from the 

 changing inclination of the land, to the higher slopes of the Wold, 

 began to advance. 



The cause of that advance, so far as it did not take place in 

 the new direction from change of inclination only, seems to receive 

 its obvious explanation in the elevation of the land from the great 

 submergence of Stage II., which by gradually exposing a loftier and 

 more extensive area of the mountain region of the north of England 

 for the interception of the Atlantic vapour, caused an augmentation 

 of the ice in taking that new direction which was the consequence 

 of the changing inclination of England ; and it was in this new 

 direction that the ice to which the Chalky Clay was due advanced. 

 Seeking the sea, the ice which descended the eastern slope of the 

 Pennine found, as it crept round the lower flank of the southern 

 extremity of that elevated region, this sea over the centre of 

 England, both nearer and in greater depth than in its old direction 

 of I^orfolk and Suffolk, while parts of its former bed in Norfolk 

 emerged, as shown in map 2 and figs. YIII. and IX. 



Sand and gravel (c) accumulated under the sea in the channels 

 formed by the ancient valleys in older formations, and those 



ice receded by increasing submergence ; so that when by this it had retreated 

 from the Chalk Wold, the Purple Clay was extruded at the time of greatest 

 depression. This view necessarily became changed when I perceived that the 

 submergence preceded both these clays, and that they were accumulated during 

 emergence. The process which I had thus attributed to the formation of the 

 Chalky Clay applies to that of the Cromer TiU and the Basement Clay of 

 Holderness, 



