264- Martinis Geological Memoh, and 



another group, on which he has conferred the name oiwealden *, 

 consisting of the Weald clay, with alternating beds of sand and 

 and of Sussex or Petworth marble; and the deposit called 

 the Hastings, or iron, sands, with its accompanying beds of 

 clay, sandstone, and calcareous grit. Descriptions of the cha- 

 racters, areas, and peculiar fossils of all these formations may 

 be consulted in the memoirs of Mantel], Martin, Webster, 

 Murchison, Dr. Fitton, and some other writers. The struc- 

 ture of the Weald is well represented in the sections of Kent 

 and Sussex, by Mr. William Smith, and explained in the 

 article on Valleys of Elevation, by Dr. Buckland, with whom 

 that term originated. 



It has been observed, by Messrs. Conybeare and Phillips, 

 that the course of the rivers watering this district, and the 

 configuration of the valleys which convey them, present a very 

 interesting geological phenomena. The great valleys of the 

 Weald were remarked to be parallel to the direction of the 

 strata ; but these do not form the channels through which any 

 of the more important streams seek the sea. These rivers 

 flow from the centre towards the north and south, at right 

 angles both to the Weald and to the strata by which it is 

 encircled, through gorges opened across the strata, instead of 

 being turned by their escarpments into the great Weald val^ 

 leys, as they would be if the fractures in these escarpments 

 were filled up. There is here displayed one of the many in- 

 stances of a double system of valleys, crossing each other 

 transversely, which the authors, from whom the preceding de- 

 scription has been abridged, were amongst the earliest to point 

 out. 



The following diagram ( fig. 129.) exhibits the geological po- 

 sition of the Weald denudation, bounded by the chalk basins 

 of London and Hampshire, " between which it lies like a 

 trough or gulley ; or like a third basin elevated between the 

 other two, and draining its waters into them through cracks 

 or channels in its sides.^' {Martin, p. 55,) By the strong 

 lines drawn from the centre of the Weald, it is intended to 

 mark the mode in which the drainage is effected. 



S, Downs. N. Downs. 



Direction of Drainage. "■"**- _^,-^'' 



x-jgit **"^ London Basin. 



The principal ravines, or transverse fissures, are observed to 

 have a remarkable correspondence on each side of the Weald, 



* It is doubtful whether either of these terms will become current among 

 geologists. 



