GREENSAND AND PALEOZOIC ROCKS UNDER LONDON. 909 



that water-bearing Greensand-beds might be found under Croydon or 

 Sydenham, or possibly still nearer London* ; for with strata 400 to 

 500 feet thick at Redhill, indicating a deep-sea basin without any 

 appearance of the proximity of land, it is evident that the shores of 

 the old Lower Greensand sea were some distance off. There is there 

 no evidence, as there is at Faringdon and in Cambridgeshire, of the 

 proximity of a shore-line. The only question was how far north of 

 Eedhill and Reigate it might be. 



This has now been settled by the section of the Tottenham-Court- 

 Road well. At Kentish Town there was no trace of any Lower- 

 Greensand beds. At the Tottenham Court Road, on the contrary, 

 they have not only set in, but have attained a thickness of 64 feet. 

 The character of the few fossils indicates waters of small depth ; 

 while the abnormal character of the strata is probably due to the 

 existence of calcareous strata of Devonian (or Carboniferous ?) age 

 in the adjacent cliffs or shore of the old Palaeozoic land. It is to these 

 that we must look for the origin of the calcareous matter which has 

 replaced in greater part the loose quartzose and ferruginous sands 

 of the Lower Greensand ; for on that old shore we might look for 

 springs such as are now met with off many limestone coasts, where 

 the shore-sands are converted into compact shelly limestones by the 

 action of freshwater springs highly charged with carbonate of lime 

 derived from the adjacent lands. 



This old shore-line must lie somewhere between the south end of 

 Tottenham Court Road and Kentish Town ; and the section between 

 the two places may be represented by the following diagram, in 

 which the Lower Greensand is assumed to end against an old under- 

 ground cliff (fig. 4). 



But whatever the origin and character of these Lower Greensand 

 beds at this well, they must merge or pass into the great beds of quartz- 

 ose sands, with their intercalated zone of Ragstone, which crop out 

 from beneath the Gault at the foot of the North Downs ; and from the 

 development which the formation has already attained in the short 

 distance between Kentish Town and Oxford Street, it is probable 

 that, with continued increasing dimensions, the sand-beds set in at 

 no great distance to the south, and that therefore the Lower Green- 

 sand will be there found in the permeable condition necessary to 

 store and transmit underground waters. 



This surmise has been to a certain extent realized on the same line 

 of country by the Artesian well recently sunk, at my suggestion, with 

 much enterprise by my neighbour H. Bingham Mildmay, Esq., of 

 Shoreham Place, near Seven oaks, and which, so far as meeting with 

 the Lower Greensand at about the estimated depth and obtaining a 

 supply of water therefrom, proved successful. Mr. Mildmay 's resi- 

 dence stands in the valley of the Darent, 12 ft. above the level 

 of the stream, 5 miles north of Sevenoaks, and 2% miles distant in 

 a straight line from the outcrop of the Lower Greensand. The level 

 of the surface above the sea is 194 ft. and of the Greensand at its 

 lowest point of outcrop about 225 ft. A shaft 25 ft. deep was first 



* " Anniversary Address for 1872," Quart. Journ. Greol. Soc. vol. xxviii. p. lx. 



