198 



EXTENT OF THE WEALDEN BEDS. 



formation ; a fact decisive of the different character of the latter 

 beds. With respect to the bones of the Plesiosaurus and the Mega- 

 losaurus, found in the Wealden beds, and also in the strata below the 

 Wealden, we know not whether the nature of these animals might not 

 fit them for living both in salt and fresh water ; it is also probable, 

 that the few scattered vertebrae found in the Wealden, may have been 

 transported by currents or inundations from more ancient rocks. In 

 the same manner, the occurrence of a few individual marine shells, 

 in a series of freshwater beds, may be satisfactorily explained. 



It may be proper to call the attention of the reader to what has 

 been before stated, respecting the submersion of the coal strata, and 

 theirbeing covered with marine formations, and again elevated; see 

 Chapter VJIl. The circumstances that attended the elevation and 

 depression of the coal strata, appear to have been similar to what 

 took place at a subsequent period in the Sussex beds or Wealden : 

 other instances of similar submergence might be given, were it ne- 

 cessary. 



While this part of the work was passing through the press, the 

 author received a copy of a Geological Sketch of the Vicinity of 

 Hastings, by William Henry Fitton, M.D. F.R.S. he. It gives a 

 brief, but very clear description of the Wealden formation, the ex- 

 tent of which Dr. Fitton has taken great pains to discover. Accor- 

 ding to this statement, the Wealden gradually becomes thinner near 

 its limits in Dorsetshire, and the interior of England. It disappears 

 westward, somewhere about Durdle Cove, on the Dorsetshire coast. 

 The existence of the Purbeck beds in the vale of Wardour has long 

 been known ; in that place Dr. F. has detected also some traces of 

 sands, corresponding to those of Hastings. " Slaty limestone, like that 

 which occurs in the upper part of the Isle of Portland, is found above 

 the equivalent of the Portland stone at Brill and Whitchurch, west 

 of Aylesbury, in Buckinghamshire, and on the coast of the Boulon- 

 nois, in France. But besides these places, Beauvais, in the interior 

 of France, is the only other locality in which any members of the 

 Wealden have yet been shown, on good evidence to exist." 



The position of the extreme points of this formation from west to 

 east, or from Lulworth Cove to the boundary of the lower Boulon- 

 nois, is about 200 English miles N. W to S. E., or from Whitchurch 

 to Beauvais, about 220 miles : the depth or total thickness, where 

 greatest, being about 2000 feet.* Dr. Fitton remarks, that this is a 

 wide diffusion of the strata, if they were the product of an estuary, 

 but by no means greater that that of many of the actual deposits, in 

 some of the larger rivers on the present surface of the globe. Dr. 

 Fitton cites the Deltas of the Ganges, the Mississippi, and the Quor- 

 ra or Niger in Africa, as presenting an extent of surface nearly equal 



* In the section it is stated at 1000 feet. 



