Ch. XIX.] TRANSYEESE VALLEYS. 273 



is siipjDOsed, that the area now occupied by the Hastings sand (jSTo. 6) 

 was once covered by the Weald clay (No. 5), and this again by the 

 Greensand (No. 4), and this by the Gaiilt (No. 3) ; and, lastly, that the 

 Chalk (No. 2) extended originally over the whole space between the 

 North and the South Downs. This theory will be better understood by 

 consulting the annexed diagram (fig. 321), where the dark lines represent 

 what now remains, and the fainter ones those portions of rock which are 

 believed to have been carried away. 



At each end of the diagram the tertiary strata (No. 1) are exhibited 

 reposing on the chalk. In the middle are seen the Hastings sands (No. 6.) 

 forming an anticlinal axis, on each side of which the other formations 

 are arranged with an opposite dip. It has been necessary, however, in 

 order to aive a clear view of the different formations, to exao-o-erate the 

 proportional height of each in comparison to its horizontal extent : and a 

 true scale is therefore subjoined in another diagram (fig. 322), in order 

 to correct the erroneous impression which might otherwise be made on 

 the reader's mind. In this section the distance between the North and 

 South Downs is represented to exceed forty miles ; for the Valley of the 

 Weald is here intersected in its longest diameter, in the direction of a 

 line between Lewes and Maidstone. 



Through the central portion, then, of the district supposed to be de- 

 nuded runs a great anticlinal line, having a direction nearly east and 

 west, on both sides of which the beds 5, 4, 3, and 2, crop out in succession. 

 But, although, for the sake of rendering the physical structure of this 

 region more intelligible, the central line of elevation has alone been in- 

 troduced, as in the diagrams of Smith, Mantell, Conybeare, and others, 

 geologists have always been well aware that numerous minor lines of 

 dislocation and flexure run parallel to the great central axis. 



In the central area of the Hastings sand the strata have undergone the 

 greatest displacement ; one foult being known, where the vertical shift of 

 a bed of calcareous grit is no less than 60 fathoms.'^' Much of the pic- 

 turesque scenery of this district arises from the depth of the narrow valleys 

 and ridges to which the sharp bends and fractures of the strata have 

 given rise ; but it is also in part to be attributed to the excavating power 

 exerted by water, especially on the interstratified argillaceous beds. 



Besides the series of longitudinal ^ alleys and ridges in the Weald, 

 there are valleys which run in a transverse direction, passing through the 

 chalk to the basin of the Thames on the one side, and to the Endish 

 Channel on the other. In this manner the chain of the North Downs is 

 broken by the rivers Wey, Mole, Darent, Medway, and Stour ; the South 

 Downs by the Arun, Adur, Ouse, and Cuckmere.f If these transverse 

 hollows could be filled up, all the rivers, observes Dr. Conybeare, would 

 be forced to take an easterly course, and to empty themselves into the 

 sea by Romney Marsh and Pevensey Levels.^; 



* Fitton, Geo], of Hastings, p. 55. f Conybeare, OutHnes of Geol. p. 8L 



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