20 -P^o/^ Sedgwick on [July, 



natural drainage of a portion of the counties of Kent and Sussex. 

 A number of small rivers take their rise in the central ridge of 

 the Hastings sands (see Greenough's Geological Map of Eng- 

 land), and descend from thence both on the north and south side 

 into the longitudinal valleys occupied by the weald clay. 

 Instead of finding their way to the sea through these valleys, the 

 rivers proceed in a direction nearly transverse to them, and escape 

 on the one side into the Thames, and on the other side into the 

 Channel, by deep gorges cut through the escarpments of the 

 "North and South Downs.* In this way the whole region is 

 intersected by a double system of valleys communicating with 

 the sea, and crossing each other nearly at right angles. It is, 

 I think, physically impossible that this singular contour should 

 have been produced by the long continued erosion of the waters. 

 For allowing that the rivers have scoured out the longitudinal 

 valleys of the weald clay, no reason can be given why they 

 should not flow down those valleys at this moment ; and on this 

 supposition it is inconceivable how they should ever have forced 

 their way (in no less than eight places) through the high ridges 

 of the North and South Downs. Again, if we suppose that the 

 North and South Downs were once prolonged to the south-east 

 so as to form a continuous ridge, we may shift the difficulty, but 

 we shall not explain it. On this supposition a large inland lake 

 might have occupied the region of the weald clay, and such a 

 lake might have burst the chalk barrier, and formed one or two 

 valleys of denudation. But it is impossible that such an agent 

 should ever have formed the complex system of valleys by which 

 the Downs are now intersected. That all these valleys have 

 been opened out by the same disturbing forces which have pro- 

 duced the accumulations of superficial gravel in the neighbour- 

 ing parts of England cannot admit of doubt. Yet we have the 

 clearest physical evidence that the drainage could never have 

 been effected by the ordinary operations of any of those disturb- 

 iug forces which are now acting on the surface of the earth. 



Drainage of the Isle of Wight. 

 The next example is supplied by the drainage of the Isle of 

 Wight.i*' Two small rivers which rise on the south side of the 

 central Downs might have escaped into the sea by low and direct 

 channels cut throu^^h the incoherent ferruginous sands. Instead 

 of this, tlu y flow into the north channel, at Cowes and Brading, 



passj ^ 

 ^'8'trp)[iOs^the^e V^n^yls to^bf^clofe^d, it is incompatible with every 



~^^^» Seith^ ^*OutMfe*«<*^tM*'G«flogy of En^and and Wales,*' p. 145. 



•f See the map accompanying Dr. Fitton's paper published in the JnnaU of Phi (a- 

 sophj/ fot ^ov. 1824. 



