400 [May 1, 



tliat place and the coast. A great portion of the two promontories 

 at Blackgang Chine belongs to this upper division ; and if the 

 interval between the bottom of the Gault within the chine and the 

 retentive stratum over which the streamlet runs to the waterfall, 

 be assigned to it, the thickness will be rather more than 200 feet, 

 including some remarkable beds — one 12 feet, and two others 

 about 17 feet each, in thickness — of fawn-coloured, or nearly white, 

 sand, not in itself distinguishable from that of Hastings, No fossils 

 from this division in the Isle of Wight have yet come to my know- 

 ledge. Its junction with the more retentive mass below appears 

 to be marked by the breaking out of springs, as in the correspond- 

 ing place near Hythe. The subdivisions of this group are detailed 

 in the drawings. 



On the coast of Kent, between Folkstone and Sandgate, this 

 upper division of the Lower Green-sand contains more calcareous 

 matter than at Blackgang- Chine, and even some concretions of 

 compact limestone, with spongy siliciferous masses, very like the 

 whetstone of Blackdown. [Geol. Trans. 2d Ser. iv. p. 118, 119.] 



§. The Gault, hitherto estimated as no more than 70 feet in 

 thickness throughout the back of the Isle of Wight, appears from 

 Mr. Simms's measurement to be 146 feet thick near Blackgang- 

 Chine. The lower part is at first view not easily distinguished, 

 from its change of colour after exposure ; but the lower line of 

 boundary was accurately traced, on the east of the hotel, by Mr. 

 Warburton, and on the west of it by myself, within the upper part 

 of the chine on both sides. On the west of the hotel, just within 

 the ravine, at the top, some of the characteristic Gault fossils, 

 including Ammonites, have been found close to the bottom of the 

 deposit ; and similar remains have been obtained, as I am informed, 

 at Puckaster. 



The much greater prominence of the Upper Green-sand, which 

 has here a thickness of 104 feet, is a very remarkable point of 

 difference from the Folkstone section. This group in the Isle of 

 Wight consists apparently of two divisions, as in Western Sussex, 

 and contains fossils in great numbers. 



§. On a general comparison of the sections of the Kentish coast 

 and the Isle of Wight, the most prominent points of difference are, 

 1st, the almost total absence of limestone at Atherfield ; and 2d, 

 the great excess, at the latter place, in the thickness, especially, of 

 the Lower Green- sand. — 



Total 1002 11 547 



So that, while the Gault in the two situations differs only 20 feet 

 in thickness, the Lower Green-sand at Atherfield exceeds that of 

 Hythe by 346 feet. There is also throughout considerable variation 

 in mineral composition, and in aspect ; but not greater than what 



