322 



PROCEEDINGS 



OF 



THE GEOLOGICAL SOCIETY. 



POSTPONED PAPERS. 



On the Age of some Sands and Iron-Sandstones on the North 

 Downs. By, Joseph Prestwich, Esq., F.R.S., Treas. G.S., &c. 

 With a Note on the Fossils ; by S. V. Wood, Esq., F.G.S. 



[Read January 21, 1857*.] 



The lower and central tracts of the valley of the Thames, from Read- 

 ing to the sea, consist of Eocene strata, with a limited covering of 

 Crag on the sea-board of Essex and Suffolk. This mass of Tertiaries 

 is skirted on the south of the Thames by a belt of chalk, which 

 rises by a gradual and continuous slope, broken by numerous small 

 transverse valleys, until it attains an average height of from 500 to 

 600 feet : it is then abruptly escarped, forming a cliif-like declivity 

 stretching east and west, and at the base of which extend the Lower 

 Cretaceous and Wealden series. This elevated chalk-tract is about ten 

 miles broad at Dover and Canterbury, and ranges westward, with a 

 variable width of six or eight miles, to Guildford, where it contracts 

 to a narrow ridge not half a mile broad. These Downs form a distinct 

 and marked division between the Tertiary strata of the synclinal 

 Thames Valley, and the anticlinal dome-plain of the Weald ; they ex- 

 hibit throughout a chalk-surface, either quite bare or covered on the 

 hill-tops by a thin capping of reddish clay, sand, and flints, with, 

 here and there, an outlier of the Lower Tertiary strata rising above 

 the general level of the chalk-plateau, and forming slightly detached 

 and more conspicuous hills. These outliers are continued at a few 

 places to the very edge of the chalk- escarpment. 



Besides the more general drift, and the few local Tertiary outliers, 

 there are, however, scattered commonly on the very summit of the 

 North Downs, from Folkestone to Dorking, a few masses of sand, with 

 subordinate gravel- and ironstone-bands, but generally so much dis- 

 turbed and so mixed up with the drift, that they appear, and have 



* For the other communications read at this Evening Meeting, see Quart. 

 Journ. Geol. Soc. vol. xiii. p. 212. 



