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CHAPTER XIII. 



PURBECK AND WEALDEN STRATA. 



AFTER the discovery by Dr. Mantell of the fresh-water 

 nature of the Hastings Sands and Weald Clay, it became 

 customary with some geologists, led by Edward Forbes, 

 to consider the PURBECK BEDS as forming the topmost 

 subdivision of the Oolites, and the Wealden strata as 

 belonging to the Cretaceous series ; but as, in reality, the 

 interval between the marked marine series of the Oolitic 

 and Lower Cretaceous epochs is, in Britain, bridged 

 over by the terrestrial and fluviatile episode of the Pur- 

 beck and Wealden beds, it is more convenient, and, in 

 the chief part of the British area, more philosophical, to 

 treat of these formations as marking one great local 

 epoch. 



For the stratigraphical arrangement of these strata 

 in the Isle of Purbeck, see fig. 75, p. 347. 



I here use the term Lower Cretaceous, in the sense 

 in which it has been applied to the Atherfield Clay and 

 Lower Greensand ever since the days of Dr. Fitton, at 

 the same time being well aware, that all the Wealden 

 strata above the Purbeck beds, and up to the top of the 

 Lower Grreensand, are the geological equivalents in time 

 of the marine Neocomian strata of the Continent of 

 Europe, though with us it happens, that the lower 

 and middle subdivisions of these beds are represented 

 by fresh-water strata in the south of England. 



