286 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 1, 



ments, like the magnesian limestone from the north of Euglaucl, used 

 for the New Palace at Westminster ; for which purpose they are oc- 

 casionally found unfit, from the presence of fragments of carboni- 

 ferous limestone, called by the workmen " cockles." The cement, 

 therefore, of this quasi-conglomerate forms the greater portion of 

 the mass ; the fragmentary matter is of rare occurrence and un- 

 rolled. In the gravel-bed of Clevedon Down, fragments derived 

 from other beds of carboniferous limestone than those on which it 

 rests, if not from older and newer rocks, form the bulk of the mass : 

 the tufaceous cement is small in quantity, and the fragments have 

 been rolled. 



I conclude by remarking, that if this gravel-bed shall prove, on 

 further investigation, to belong to an era more remote than the pleis- 

 tocene, it will by no means invalidate my argument respecting the 

 southern extension of the glacial sea beyond the limits which have 

 been assigned to it ; for that extension rests on a variety of inde- 

 pendent evidence enumerated in the commencement of this paper. 



2. On the Origin of the Soils which cover the Chalk of Kent. 

 Part 3. By Joshua Trimmer, Esq., F.G.S. 



[For Parts I. & II. see Quart. Journ. Geol. Soc. vol. vii. p. 31, and vol. viii. p. 273.] 



[Plate XIII.] 



We have been recently indebted to Sir Roderick Murchison * and 

 Mr. Martin t, of Pulborough, for valuable additions to our knowledge 

 of the superficial deposits of the South-eastern counties, within the 

 area of the Weald, and also exterior to it, both on the North and the 

 South Downs. 



Mr. Martin J divides the detrital accumulations upon the Chalk 

 into two zones, which he calls the tertiary and the cretaceous, — the 

 former, both on the north and on the south, the most remote from 

 the escarpments of chalk which bound the Weald. 



He describes the tertiary zone as composed chiefly of rolled pebbles, 

 derived from the eocene tertiaries. Eocene pebbles, on the contrary, 

 enter sparingly into the composition of the cretaceous zone ; which 

 consists, he says, chiefly of whole or fractured flints, passing occa- 

 sionally into beds of loam and patches of chalk rubble. In this de- 

 scription I concur, as to that portion of the chalk which I have 

 examined, subject to this qualification, — that the deposits of the 

 cretaceous zone intrude into the area of the tertiary zone, and replace 

 it, wherever it has been much denuded. 



It is to this tertiary zone, in the district between Shooter's Hill 

 and the Medway, that I wish to draw attention in the present com- 

 munication, as containing pebbles of distant origin, derived from the 



* Quart. Journ. Geol. Soc. vol. vii. p. 349. 



i Philosophical Magazine, 4th series, vol. ii. 1851. J Ojj. ciL 



