228 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 25, 



the range of these two strata a few hundred feet to the eastward, 

 the sand is found to pass from yellow to ash colour and to thin 

 out, whilst the overlying clay swells out and attains a thickness of 

 twelve to fourteen feet. 



The beds below the London clay from Barton to Poole harbour 

 and Stutland consist almost entirely of sands: the same beds at 

 Alum Bay show nearly equal proportions of clay and sand, whilst 

 at White Cliff Bay the clays are to sands about as two to one. 

 The thick strata of mottled clays and brown clays (" b and d ") at 

 Alum Bay are not exhibited at Stutland; or if, as I rather presume 

 them to be, they are hidden by the slope and talus of the cliff, their 

 thickness must be very inconsiderable. 



On the whole, it is evident that siliceous sands preponderate to 

 the westward and clays to the eastward, and that in the fluvio-ma- 

 rine deposits calcareous and siliceous rock strata are, in the lower 

 division, most fully developed on the north side of the Isle of Wight, 

 and, in the upper division, at Headon Hill. 



Another point that may be further briefly noticed in connexion 

 with the changes in lithological character is the frequent and con- 

 siderable variation in the thickness of most of the strata. At Alum 

 Bay the mottled clays " h " are 90 feet thick, and at White Cliff 

 Bay as much as 140 feet. So also at the former place stratum 

 "c?" is 195 feet thick, whereas at the latter place it is about 300 

 feet thick. The succeeding sands and London clay at Alum Bay 

 are 1020 feet in thickness, and at White Cliff Bay 820 feet. The 

 Lo\ver Headon Hill sands at the former place measure 120 feet, 

 and at the latter 195 feet. At Headon Hill the lower division of 

 the fluvio-marine series is but seventy feet thick, whereas at White 

 Cliff Bay it attains a thickness of 350 feet. The upper division of 

 this last group is more important at Headon Hill, but not beinuj in 

 either case complete, will not admit of accurate comparison. The 

 result of two measurements of the series included between the chalk 

 and the upper division of the fluvio-marine group (known as the 

 upper marine formation) gave at Alum Bay 1500 feet, and at White 

 Cliff Bay 1800 feet. My object in alluding to these facts is to show 

 the irregular and active conditions prevailing during the accumula- 

 tion of these tertiary strata, which it is important to bear in mind 

 in examining their organic remains, whose distribution exhibits 

 material corresponding modifications. 



Organic Bemains* 



Neither in the thin bed of sand immediately overlying the chalk, 

 nor in the succeeding thick beds of mottled clays "6," have any 

 animal remains been hitherto found, so far as I am aware, either at 

 Alum Bay or White Cliff Bay. But at both places the mass of brown 

 sandy clay " d " overlying the mottled clays is well-characterized by 

 peculiar fossils. At Alum Bay their existence has been long known. 

 iMr. Webster noticed them in 1816, Mr. Sowerby in 1821, Prof. 



