182 THE ORIGIN OF THE VALE OF MARSHWOOD. 



it came to pass that a wide tract of clay was gradually exposed over 

 the western part of the periclinal area, while to the southward the 

 rivers pass through valleys with steep slopes on each side, the 

 intervening tracts rising into a succession of hills, some of which 

 are capped by patches of Inferior Oolite and others by remnants 

 of the original covering of Greensand. 



These southern hills are well seen by anyone standing at the 

 foot of Pilsdon Pen, and they look as if they would present an 

 impassable barrier to any river running southward from the 

 watershed on which the observer stands. 



The rivers which now drain the district are the Char and the 

 Simene, while the Brit drains the eastern part of the periclinal 

 area, and they all make their way through gaps in the southern 

 hills. But, besides the valleys of these rivers, there is a wide gap 

 at the head of the valley of the little river Chid, which runs 

 through Chideock, and I think it probable that this gap was part 

 of the valley of a river which had a more northern source. There 

 is little doubt that in some cases one river-system extended itself 

 at the expense of another, the lateral tributaries of the one en- 

 croaching on the area drained by the other, and sometimes entirely 

 cutting off or capturing the headwaters of the adjacent river.* 



The present course of the Char is so different from the com- 

 paratively straight courses of the Simene and the Brit, that it 

 suggests the idea of its having absorbed the tributaries of an 

 eastern neighbour. The col at the present head of the Chideock 

 valley does not rise above 250 feet, the hills on each side being 

 double that height, and I am inclined to think that there was a 

 time, before the valleys were carved out to their present depth, 

 when three rivers traversed the Vale of Marshwood, and that the 

 ancestor of the Chid was one of them. The final sculpturing of 

 the country took place during and soon after the close of the 

 Glacial Period, and it was probably then that the capture by the 

 Char of the upper tributaries of the Chid was accomplished. 



* Fora case in Lincolnshire described by the Author see Quart. Jouni. 

 Geol. Soc., Vol. 39, p. 596, 1883. 



