346 



WEALD CLAY. 



[Cir. XVIII. 



is unequivocal $ the Weald Clay being distinctly seen to pass beneath 

 the Lower Greensand in various parts of Surrey, Kent, and Sussex, 

 and to reappear in the Isle of Wight at the base of the Cretaceous 

 series, being, no doubt, continuous far beneath the surface, as indicated 

 by the dotted lines in the annexed diagram, fig. 337. 



Fiar. 



Isle of Wight. 



Hants. 



Sussex. 



a. Chalk. &. Greensand. c. Weald Clay. d. Hastings Sand. e. Purbeck Beds. 



The Wealden is divisible into two minor groups : 



Greatest known 

 thickness. 

 1st. Weald Clay — blue and brown clay and shale, sometimes includ- 

 ing thin beds of sand and shelly limestone with Paludina, 600 feet. 

 2d. Hastings Sand — chiefly arenaceous, but in which occur some 



clays and calcareous grits,* ----- ^40 " 



Another freshwater formation, called the Purbeck, consisting of vari- 

 ous limestones and marls, containing distinct species of molluscs, Cyp- 

 rides, and other fossils, lies immediately beneath the Wealden in the 

 south-east of England. As it is now found to be more nearly related, 

 by its organic remains, to the Oolitic than to the Cretaceous Series, it 

 will be treated of in the twentieth chapter. 



Weald Clay. 



The upper division, or Weald Clay, is of purely freshwater origin. 

 Its highest beds are not only conformable, as Dr. Fitton observes, to 

 the inferior strata of the Lower Greensand, but of similar mineral 

 composition. To explain this, we may suppose, that, as the delta of 

 a great river was tranquilly subsiding, so as to allow the sea to en- 

 croach upon the space previously occupied by freshwater, the river 

 still continued to carry down the same sediment into the sea. In 

 confirmation of this view it may be stated, that the remains of the 

 Iguanodon Mantelli, sl gigantic terrestrial reptile, yerj characteristic 

 of the Wealden, has been discovered near Maidstone, in the overly- 

 ing Kentish rag, or marine limestone of the Lower Greensand. Hence 

 we may infer, that some of the saurians which inhabited the country of 

 the great river continued to live when part of the country had become 

 submerged beneath the sea. Thus, in our own times, we may sup- 

 pose the bones of large alligators to be frequently entombed in recent 



* Dr. Fitton, Geol. Trans., Second Series, vol. iv. p. 320. 



