"Vol. 50.] ARTESIAN BORING NEAR WINDSOR FOREST. 155 



reaching levels between 800 and 900 feet above Ordnance datum. 

 For example, the broad plateau of Hindhead, south of Farnbam, 

 reaches an elevation of about 900 to 910 feet where crossed by one 

 of the sections of the Geological Survey (Sheet 73) ; also at the 

 Royal Huts Inn the surface rises to 840 feet, and at Gibbet Hill to 

 895 feet, according to the Ordnance Survey. The average level of 

 this broad tract of Lower Greensand about Haslemere may be taken 

 at about 600 feet, which is nearly 400 feet higher than the surface 

 of the ground at the boring at New Lodge, Windsor ; so that we can 

 account for the great hydrostatic pressure of the water at this spot, 

 notwithstanding the long distance that it has to travel through the 

 mass of the formation itself. Doubtless the whole formation under 

 the Chalk is waterlogged ; but it should be recollected that when 

 reached by a well or borehole the supply derived from the imprisone d 

 water in the underground reservoir may gradually fall off, and the 

 supply then becomes dependent on the annual percolation. This has 

 been found to be the case with wells in the New Red Sandstone. 



Discussion. 



The President said it was satisfactory to l^arn that there was an 

 area near West London in which the Lower Greensand was full of 

 water. He thought that the section exhibited by the Author ex- 

 plained why it was full in that particular locality, for the rainfall 

 about the extensive area of Hindhead, which lay nearly due south, 

 must be considerable. 



Mr. W. J. Lewis Abbott wished to ask if Prof. Hull had any 

 absolute data upon which to bring up this Palaeozoic ridge to 

 within 200 feet of O.D., as shown in the section. He would be 

 glad to know whether, in the boring, the Folkestone Beds showed any 

 lithological change, such as would be expected, had that part of the 

 beds been deposited along the shallow sea of a Palaeozoic island- 

 ridge. The extended outcrop of the Greensands was quite sufficient 

 to account for their superior yield of water. 



Mr. W. Whitaker also spoke. 



The Author replied. 



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