THE WEALDEN STRATA. 269 



The total thickness of the Wealden (inclusive 

 of the Purbeck beds) is estimated at upwards of 

 1,500 feet, being equal to three times that of the 

 delta of the Mississippi."* 



Wealden strata of the Isle of Wight. — 

 In the Isle of Wight but a small portion of the 

 upper series of clays, sands, and sandstones is ex- 

 posed to view. These deposits constitute the line 

 of coast already noticed, in San down Bay, and 

 the range of cliffs from near Atherfield Point to 

 Compton Bay. The section exposed in the cliff's 

 on the south-western coast, is shown in lign. 16, 



from the strata of the Weald. Having for several years diligently collected 

 the fossils of the south-east of Sussex, and separately arranged the specimens 

 from different localities, I was struck with the want of accordance between 

 the organic remains from the chalk, gall, hrestone, &c. and those which I had 

 obtained from the quarries and wells, opened or sunk in the Wealden district , 

 and by degrees, the freshwater character of the area between the green sands 

 of Sussex, Kent, and Surrey, became manifest. The absence of ammonites, 

 echinites,terebratulas, corals, and otiier common and characteristic fossiis of the 

 chalk, in my wealden collection, was a circumstance that could not fail to arrest 

 attention; and the discovery of the bones of large reptiles, witli the leaves 

 and stems of ferns, cycadeous plants, &c. in the strata of 'lilgate Forest, of 

 which there were not the slightest traces in the cretaceous deposits, corro- 

 borated the inferences suggested by my previous observations. In 1S22 the 

 Tilgate strata were first described, and their freshwater origin pointed out in 

 " The Fossils of the South Downs." In June 1822, I communicated to the 

 Geological Society of London an account of the extension of these strata over 

 Sussex, being the result of my own and Mr. Lyell's observations. In 1827, 

 "The Fossils of Tilgate Forest," containing nearly 200 figures of wealden 

 fossils, was published. See Dr. Fitton's charming little work ; "A Geological 

 Sketch of the vicinity of Hastings." London, 1832. p. 13. 



* The delta of the Mississippi is computed by Mr. Lyell to be 528 feet, or 

 about the tenth of a mile in depth; the area it covers 13, COO square statute 

 miles ; the solid matter annually added 3 billions 700 millions cubic feet ; and 

 the period required for its formation, many thousand years. 



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