of the Iguanodon in the Isle of Wight and Isle of Portland. 429 



of the sections in Conybeare and Phillips's Geology of England. As this 

 iron-sand here extends along- almost a mile of coast^ and through great part of 

 the distance is inclined at an angle varying from 15° to 30° N., its thickness 

 must be very considerable. After making all due allowance for the possible 

 occurrence of faults, I cannot estimate it at less than 500 feet, which is the 

 reputed thickness of this formation in the Weald of Sussex and Kent, 



Dr. Fitton, in his excellent paper in the Aim, Phil. November 1824, has 

 drawn an interesting comparison between this iron-sand at Swanwich, and 

 the iron-sand of Sandown Bay in the Isle of Wight, and of Tilgate Forest; 

 and has shown that there is a nearly perfect correspondence in the characters 

 of the strata of this formation in Purbeck, with those which they present in 

 the Isle of Wight, and in the Weald of Sussex ; and that in each case they 

 are immediately covered by the Weald clay, and contain occasionally the 

 same admixture of the remains of marine animals with those whicli were 

 inhabitants of fresh water*. 



Mr. Conybeare, also, and Mr. Mantell, have consideied the argillaceous 

 limestones which lie below these iron-sands in Sandown Bay, and form the 

 lowest strata in the Isle of Wight, to be nearly identical with the shelly 

 bivalve limestone beds of Ashburnham, and to afford at both these places an 

 equivalent to the upper freshwater strata of the Purbeck series. 



It is satisfactory that in three such important localities as Sandown Bay, 

 Brook, and Swanwich Bay, we have ascertained the presence of an animal so 

 very remarkable as the Iguanodon, whose existence has not till now been 

 traced beyond the Weald of Sussex ; and it is still further satisfactory, to 

 find, that in tending to identify the iron-sand of Purbeck and the Isle of 

 Wight with that of Hastings and the Weald, these additional discoveries 

 confirm the opinions of our best geological authorities. 



It has been inferred, from the mixed nature of the remains occurring in 

 this formation, that the area on which it was deposited was at that time part 

 of a great estuary ; the facts we have been considering show that the extent 

 of this estuary was continuous to the south-west, and west, from the Weald of 

 Sussex, through the districts now occupied by the Isle of Wight, to the Isle of 

 Purbeck in Dorsetshire. The strata of tlie Purbeck formation at Lady Down 

 near Tisbury, show that it included, also, the south-west extremity of Wiltshire. 



We know not what are the fundamental strata of any portion of this district, 

 except at its western extremity, where the Wealden and Purbeck freshwater 

 series rest upon the oolitic marine formation of the Portland stone. 



* See Dr. Fitton's Map and Sections, Ann. Phil. 1824, N. S. vol. viii. PI. XXXIII. 

 VOL. Ill, SECOND SERIES. 3 K 



