S88 DENUDATION AND SCENERY. 



fact to abut against the Devonian, Carboniferous, and Granitic 

 rocks of Devonshire, if not also against the older rocks further 

 north. It is difficult to say to what extent the older rocks were 

 buried up by these Cretaceous sediments, but probably the Chalk 

 itself overspread the greater part of what is now England and Wales. 



As we pass from the Cretaceous to the Eocene period, we begin 

 to discern the framework of much of our present scenery. The 

 Chalk which stretched far west was upheaved on that side, while 

 it was covered by much sediment and suffered much destruction 

 to the south and east ; for Chalk cliffs must have been formed on 

 the margin of the Eocene seas. At the same time, rivers of con- 

 siderable magnitude helped to denude the Chalk inland, and to 

 bring down muddy sediments from the higher ranges of the hills. 

 This was also the case in the Bovey Basin, and later on in Upper 

 Eocene or Oligocene times, when estuarine and freshwater con- 

 ditions for a time prevailed. Then great disturbances took place 

 whereby the Chalk and Lower Tertiary strata of the Isle of Wight 

 and Dorsetshire were uptilted and folded along the remarkable 

 uniclinal axis they now present ; and the Wealden and other anti- 

 clinals were produced. (See p. 426.) These disturbances, followed 

 by denudation, led to the formation of the North and South Downs, 

 and to the separation of the London and Hampshire Basins. 

 Thus the lie of the Secondary strata and their general south- 

 easterly inclination has had a marked effect on the configuration 

 of the land, modified as it is by the undulations in the southern 

 and eastern counties. 



The denudation of the Chalk tracts was partly carried out 

 in later Eocene and Miocene times by subaerial agencies ; and 

 extensive sheets of loose flint-gravel and clay-with-tlints may then 

 have been formed. 



In Pliocene times the sea spread over portions of the south and 

 east of England, in the latter area forming cliffs in the London 

 Clay and Chalk, the debris of which helped to make up portions 

 of these newer Tertiary strata : but no remains of these old cliflf- 

 lines are preserved. 



The only evidences we have of river-deposits in Pliocene times 

 are in the Fluvio-marine portions of the Crags, and in the Cromer 

 Forest Bed Series. In the latter case England formed part of the 

 continent, and the Thames, if it then existed, joined its waters 

 to an extension of the Rhine, which flowed over what is now the 

 North Sea. No Pliocene deposits have, however, been met with 

 in the Thames valley. Then came the Glacial epoch, with its 

 mantles of ice, its coast-ice, and ice-bergs, spreading far and wide 

 the material derived from many a formation, and re-depositing old 

 superficial accumulations, due to the waste of the land by subaerial 

 agents in previous ages. The valley of the Severn was probably 

 much enlarged at this period, while the Thames must have marked 

 out its course much as it is now.' 



During the Glacial Period old river-valleys were in many 



' See J. G. Goodchild, P. Geol. Assoc, ix. 153. 



