88 GEOLOGY OF THE ISLE OF WIGHT 



present position proves that the same movement was con- 

 tinued at a later time, probably during the Pleistocene. 

 But the greater part of the movement may be assigned to 

 the Miocene, the period of great world-movements which 

 raised the Alps and the Himalaya. 



Many remarkable, and, at first sight, very puzzling 

 features connected with the courses of rivers find an 

 explanation when we study the river history. Thus, 

 looking at the Weald of Kent and Sussex, we see that it 

 consists of comparatively low ground rising to a line of 

 heights east *-nd west along the centre, and surrounded 

 on all sides but the south-east by a wall of Chalk downs. 

 If we considered the subject, we should suppose that the 

 drainage of the country would be towards the south-east, 

 which is open to the sea. Not so. All the rivers flow from 

 the central heights north and south, go straight for the 

 walls of chalk downs, and cut through the escarpment in 

 deep clefts to flow into the Thames and the Channel. 

 This is explained when we remember that the rivers began 

 to flow when the great curve of strata rose above the sea. 

 Though eroded by the sea during its elevation, yet when 

 it rose above the waters the arch of chalk must have been 

 continuous from what are now North Downs to South. 

 And from the centre line of the great turtle back the 

 streams began to flow north and south, cutting in the 

 course of ages deep channels for themselves. The greater 

 erosion in their higher courses has cut away the mass of 

 chalk from the centre of the Weald, but the rivers still 

 flow in the direction determined when the arch was still 

 entire. 



We have a similar state of things in the Isle of Wight. 

 Any one not knowing the geological story, and looking at 

 the geography of the Island, might naturally suppose 

 that there would be a stream flowing from west to east, 

 through the low ground between the two ranges of downs, 

 and finding its way into the sea in Sandown Bay. Instead 



