6 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 21, 



showed that from Lewes Levels to Chichester Harhour, and on to 

 Hurst Castle, the coast exhibits signs of undergoing elevation at the 

 present day. The coast of the Isle of Wight opposite seems, on the 

 contrary, to be suffering depression ; whilst the back of the island 

 exhibits some curious signs of local oscillation. 



November 21, 1855. 

 James Gay Sawkins, Esq., was elected a Fellow. 

 The following communications were read : — 



1. On the Boring through the Chalk at Kentish Town, 

 London, By J. Prestwich, Esq., F.R.S., Sec. G.S. 



It is little more than half a century since Artesian wells were brought 

 into use in and around London. The success of the first works led 

 to so rapid an extension of this mode of procuring water that the 

 source of supply, which was from the sands under the London Clay, 

 proved insufficient for the demand. Consequently, in order to ob- 

 tain a better supply of water, a large number of the wells more re- 

 cently constructed have been carried down to variable depths into 

 the underlying chalk. Nevertheless, the water-level in the Artesian 

 wells, which, in 1822, rose to the level of Thames high-water-mark, 

 now stands in London at about 50 feet below that level, and continues 

 to fall at the rate of about 1|^ to 2 feet annually. 



From a previous acquaintance with the London Tertiary district, 

 and from the attention which the question of the water-supply 

 attracted at the time, I was led, in 1849, to make some inquiries 

 into the bearing of the geological structure of the country around 

 London with reference to the question of the deep-well-supply. The 

 result of that inquiry I published early in 1851 *, and the conclusion 

 to which I arrived was that the dimensions of the Lower Tertiary 

 sands were insufficient to furnish any increased supply, and that the 

 chalk not being, properly speaking, a water-bearing deposit, i. e. one 

 transmitting water freely in all directions through its mass, could 

 only yield at that depth beneath the surface, and from its outcrop, 

 an uncertain and moderate supply. I further showed, that from be- 

 neath the chalk there cropped out, both to the north and south of 

 London, a large mass of light-yellow, ochreous, and white siliceous 

 sands, geologically known as the Lower Greensand, 300 to 500 feet 

 thick, extremely permeable, and yielding generally, in its surface- 

 wells and springs, water of good quality. As I found that the 

 effective area and thickness of this deposit was ten times greater 

 than that of the Lower Tertiaries, and its outcrop considerably higher, 



* " A Geological Inquiry respecting the Water-bearing Strata of the country 

 around London." 8vo. Van Voorst, 1851. 



