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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 25, 



June 25, 1851. 



Lieut. H. U. Tyler, R.E., was elected a Fellow ; and Signor An- 

 gelo Sismonda was elected a Foreign Member. 



The following communications were read : — 



1. On the Drift at Sangatte Cliff, near Calais. 

 By J. Prestwich, Jun., Esq., F.G.S. 



The flat and extensive plain around Calais is composed of Tertiary 

 strata (bearing a close resemblance to the London series), reposing on 

 Chalk and overlaid by a thick covering of flint-gravel. At the small 

 village of Sangatte, three miles W.S.W. from Calais, and immediately 

 opposite to Dover, the chalk rises to the surface, forming the well- 

 known promontory of Blanc-nez. These chalk cliffs were described 

 in the Transactions of the Geological Society for 1820 * by Mr. W. 

 Phillips, who alludes briefly to the large accumulation of flint-gravel, 

 and observes " that this kind of deposit is confined to the summit of 

 the rising cliff, which consists beneath of sand lying in thin beds of 



different colours " "but the general tint of the mass is greenish/' 



He continues — " the probability that this sand may belong to the 

 Plastic Clay formation occurred to me, but I discovered nothing 

 beyond the general appearance of the sand to strengthen the suspi- 

 cion." He correctly notices that this newer deposit abuts against 

 the Chalk. In 1839, M. D'Archiac also noticed these cliffs, and 

 stated that they exhibited a flint-gravel 8 metres thick, overlying 3 

 metres of a yellowish sandy clay with fragments of chalk — the whole 

 reposing on a bed of deep greenish coloured sand about 3 metres in 

 thickness, unconformable to the Drift above f, and apparently belong- 

 ing to the Sables Inferieurs, but without fossils to prove it. 



When passing through Calais last autumn, I visited Sangatte, for 

 the purpose of examining these reputed Tertiary strata ; but either 

 they have been removed by the wearing away of the cliff, or else the 

 greater distinctness of the section prevents me from feeling the doubts 

 expressed by the above-named geologists, — the section, as it now exists, 

 apparently consisting entirely of a variable mass of Drift, bearing a 

 striking resemblance to that of the cliff at Brighton, described by 

 Dr. Mantell in 1833 J, and more recently by Sir R. Murchison§. In 

 general structure, colour, materials, and order of superposition, the 

 character of these cliffs is so much alike, that a section of the one 

 might almost pass for that of the other. At the base of the Sangatte 

 Drift, and reposing upon a ledge of Chalk (see Section), is a bed 

 varying from 4 to 8 feet in thickness, and consisting of black chalk- 

 flints, mostly rather large, and all a good deal rolled and worn, but 

 not rounded. With these are some large flattish worn masses of chalk. 

 The whole is loosely mixed with a very small quantity of sand. The 

 peculiar character of this bed is the uniformity of wear and the water- 



* Vol. v. p. 47. t Memoires Soc. Geol. de France, t. iii. p. 263. 



t Geology of the South-East of England, p. 31. § May 1851. 



