80 



MR. E. PEOCTOE ON I'OSSILIEEEOTJS OLD EED [March I913, 



some of them may be sections of calcareous algse built up of a 

 number of fine tubes. Calcareous SipJionice are certainly known 

 from as far back as the Devonian Period. 



Eecord of Rocks passed through. 



The record of the boring given by Messrs. Isler is as follows : — 



Made ground 



and 



alluvium. 



London Clay ... 



Lower London 



Tertiaries, 



inclu cling 



Thanet Sands. 



Chalk .... 



Gault .... 

 Devonian 



f Brown clay 



-( Gravel and sand 



l_Brown clay 



Blue clay 



Black pebbles 



Mottled clay 



Yellow mottled clay 



Mottled clay and pebbles. 



Sandy mottled clay 



Dark sandy clay 



{ Loamy green sand 



f Chalk 



\ Grey chalk 



Blue Gault 



Bed marl 



Thickness 



Depth 



in feet. 



in feet. 



6 



6 



20 



26 



1 



27 



196 



223 



1 



224 



16 



240 



10 



2o0 



12 



262 



22 



284 



3 



287 



8 



295 



107 



402 



466 



868 



262 



1130 



97 



1227 



[This record would appear to have been made when the boring had only 

 reached 1227 feet. A record of the boring, with a slight variation in the figures 

 for the Chalk and Gault, has been published by the Geological Survey since 

 the reading of this paper: see ' Eecords of London Wells' Mem. Geol. Surv. 

 1913.] 



Conclusions. 



(1) The absence of anything corresponding to the Lower Green- 

 sand might perhaps have been anticipated. In his Presidential 

 Address to the Geological Society in 1900 l Mr. "W. Whitaker pointed 

 out that, while this formation is present in all the borings east of 

 the River Darent in Kent, it is thinning towards the west. It is 

 present at Crossness, and is only 10 feet thick at Richmond. As the 

 Lower Greensand is absent at Southali, it appears strange that it is 

 present at Slough in sufficient thickness to yield large quantities of 

 water. 



In this connexion, it is interesting to notice that Sir Joseph 

 Prestwich 2 held the view that the old Palaeozoic land was of the 

 nature of a ridge, with breaks in it at intervals. He wrote : — 



' I cannot imagine but that, from the very peculiar mineral character of the 

 mass in Bedfordshire and Surrey, there must have been, in places, continuity 

 between these areas, and 1 therefore infer that the Lower Greensand may yet be 

 found under the Chalk at many places, and that, although not immediately 

 under the north of London, it yet will be found at no great distance both to 

 the north and south of that spot.' 



1 Q. J. G. S. vol. Ivi (1900) pp. lxxviii-lxxix. 



2 Ibid. vol. xiv (1858) pp. 251-52. 



