Geological Society. 221 



formation passing from the coast of Dorsetshire, round the Black- 

 down hills in Devonshire, and thence by the vales of Wardour, 

 Warminster, and Pewsey, through Oxfordshire, Buckmghamshire, 

 Bedfordshire, &c. to Hunstanton Cliff on the coast of Norfolk, where 

 the course of the chalk range is interrupted by the sea. These sec- 

 tions prove that the order of the strata is throughout the same as m 

 the Isle of Wight, and in Kent, Surrey and Sussex ;-and the paper 

 describes the principal variations in the proportions and characters 

 of the beds, at the site of the several sections , , , ... 



In proceeding westward from the Isle of Wight, the beds which 

 intervene between the chalk and the Purbeck limestone appear to 

 run together ; and cannot well be distinguished further west than 

 Lulworth Cove. Beyond that point no trace has yet been detected ot 

 any of the freshwater beds beneath the lower green-sand ; nor is the 

 separation of the upper from the lower of these sands by a stratum 

 of clay ( Gault) any longer discernible. Some fossils, however, of the 

 eault occur in the sands on the coast near Lyme Regis, and at the 

 well-known quarries of Blackdown ; and the presence of the gault 

 itself beneath the upper green-sand is again distinct in the Vale ot 

 Wardour, and throughout the entire range from thence to Norfolk. 



The only places in which the author has detected the presence 

 of the freshwater beds succeeding the lower green-sand, are in the 

 Vale of Wardour, and in the vicinity of Aylesbury : and it would 

 appear that the great extent of the sands immediately beneath 

 the chalk, shooting out beyond the subjacent strata, and concealing 

 their outcrop, may be one cause why the group next in succession 

 is but rarely visible in the interior ;-though it is also probable that 

 strata produced at the bottom of freshwater-lakes, or of aestuaries, 

 were originally deposited in detached portions, comparatively of no 



great extent. _ . r i n\ ^^ o 



In the Vale of Wardour, the series consists of,— 1. Clialk; /. 

 Upper green-sand; 3. Gault; 4. Traces of the lower green-sand 

 (Shanklin sands) ; 5. Traces of the Hastings sands ; 6 the Purbeck 

 strata,-containing in great abundance freshwater shells, principally 

 of the genus Cyclas, and in the upper part the Cypris faba : which 

 remarkable fossil therefore pervades the whole group between the 

 lower green-sand and the Portland stone ; 7. Calcareous strata, con- 

 taining the fossils of the Portland stone, and of the same mineralo- 

 gical character with the beds of that formation in the Isle ot Pur- 

 beck ; 8. Clay, like that of Kimmeridge, &c. 



The succession in the vicinity of Aylesbury is nearly the same 

 with that of the Vale of Wardour ; the Portland stone being covered 

 at Whitchurch by beds of whiteish fissile limestone, containing 

 freshwater shells, among which are Cyclades, and a species of Cypris. 

 The Portland strata occur also at Brill Hill in Buckinghamshire, and 

 at Garsington in Oxfordshire; and the remarkable nodules of bhot- 

 over-hii:, lliough differing considerably in appearance from the lime- 

 stone of Portland itself, must probably be referred either to that 

 formation, or to a group of strata which, from their aboundmg in 

 green particles, might be confounded with some of the calcareous 

 beds of the lower grccn-sand, but which, both in Buckinghamshire 



and 



