GENERAL TOPOGRAPHY 133 



Country, and in Wales. By a later series of plications 

 the younger Palaeozoic rocks were thrown into ncrth- 

 and-south and east-and-west ridges, the latter of which 

 still powerfully affect the topography in southern Ire- 

 land, and thence through South Wales and Belgium. 

 An east-and-west direction was followed by the more 

 important subsequent European disturbances, such as 

 those that upheaved the Pyrenees, Jura, and Alps. 1 

 Some of the latest movements that have powerfully 

 affected the development of our scenery were those 

 that gave the Secondary rocks their general tilt to 

 south-east. It is very doubtful if any part of the 

 existing topography can be satisfactorily traced back 

 beyond Middle or Older Tertiary time. 2 The amount 

 of erosion of some of the hardest rocks of the country 

 since that date has been prodigious, as may be seen 

 in the fragmentary condition of the volcanic plateaux 

 of the Inner Hebrides. 



GENERAL TOPOGRAPHY. 



The main topographical features of Britain may be 

 arranged as mountains, tablelands, valleys, and plains. 

 All our Mountains are the result of erosion on areas 

 of land successively upheaved above the sea. In the 

 development of their forms, the general outlines have 



1 To these east-and-west foldings of the terrestrial crust we owe 

 the plication of our Cretaceous and older Tertiary strata which have 

 given us the ranges of the North and South Downs. They were 

 accompanied by powerful horizontal thrusts of portions of the 

 crust. The successive plications of the terrestrial crust in the 

 European area have since been discussed by Prof. Suess in his 

 Antlitx der Erde. 



2 See note on p. 146. 



