represented as alternating with freshwater beds full of Paludinoe and other Wealden fossils. This series of fossils was presented to the Society by D. D. Heath, Esq.
2. Hythe. At this place Mr. Mackeson discovered, about 30 feet below the top of the Weald Clay, beds of limestone crowded with oysters * ; and similar beds in a like position have been noticed by Mr. Simms and other observers†.
VI. Relations or the Punfield Formation to the Wealden, Neocomian, and Cretaceous of the South of England.
1. Unconformity between the Cretaceous and Neocomian. — We are indebted to the late Captain Ibbetson for first clearly demonstrating the existence of an unconformity between the Cretaceous proper and the Neocomian in the South of England‡. By a series of careful trigonometrical observations he showed that, while the Chalk, Upper Greensand, and Gault beds in the south of the Isle of Wight are nearly horizontal, the Neocomian and Wealden dip to the east at an angle of about 2°. The effects of this unconformity are most striking, the beds of Cretaceous age overlapping in succession all the beds of the Oolite and Lias, and resting, in Devonshire, on the New Red. The same effect of overlap through unconformity was, at an earlier date, demonstrated in Yorkshire by the labours of Smith and Phillips ; and I have shown that the same phenomenon is exhibited in Lincolnshire. The work of the Geological Survey has proved that a similar overlap of the Cretaceous occurs all round the Weald, and throughout the Midland district, so far as the survey has been carried. Every geologist is familiar with the fact that the same phenomenon of unconformity is exhibited between the Cretaceous and Neocomian strata of France and Switzerland. Professor Ramsay has shown from Mr. Etheridge's Tables that this unconformity is accompanied by a very great change between the faunas of the two series of strata §.
2. Variation in character of the Cretaceous in proceeding from East to West. — That the "Upper Cretaceous does not terminate downwards with the "junction-bed" at the base of the Gault Clay has been noticed by several geologists, who have shown that the sands immediately below that clay contain characteristic species of Gault Ammonites. That the same is true of the corresponding beds on the east side of the Paris basin, is shown by the able researches of M. Cornuel, in the department of the Haute Marne ||. As the base of the true Cretaceous and the top of the Neocomian are thus alike composed of sands which are usually very unfossiliferous, it often becomes a question of great difiiculty where the boundary
- Mem. of Geol. Survey, Geology of country between Folkestone and Rye,
by F. Drew (1864), p. 6.
† Proc. Geol. Soc. vol. iv. p. 208.
‡ Quart. Journ. Geol. Soc. vol. iii. p. 315.
§ Quart. Journ. Geol. Soc. vol. xx. p. 58.
|| Bull, de la Soc. Geol. de France, 2 e ser. tome. xvii. p. 743 ; Wiltshire, Quart. Journ. Geol. Soc. vol. xxiv. p. 483, in Discussion.
VOL. XXVII. PART I. R
