1XXXV1 PKOCEEDINGS OP THE GEOLOGICAL SOCIETY. [May I9OO,. 



than that from which the name is taken), our increased knowledge 

 is less and goes down to a less geological depth. 



We have certainly learnt much as to the thickness of various 

 divisions of the Tertiary both in Sussex and in Hampshire, and 

 also of their underground extension, especially under the far- 

 spreading mantle of Drift that reaches for some miles inland 

 from the coast in great part of the former county, as shown 

 on the new Geological Survey maps. The old maps indeed must 

 often have been mere guesses in this matter, no evidence having 

 been then obtained over the vast flat surface of the Drift tract. 



We have, of course, at the same time learnt something of the depth 

 to the Chalk, through the Eocene Tertiaries ; but only by means of 

 some 22 wells and borings in Sussex and as many in Hampshire. 

 This small total of 44 is not an eighteenth of that in the London 

 Basin. 



As to the thickness of the Chalk under the Tertiary in the 

 Hampshire Basin, this was known before the time of which I 

 have been treating, by the boring at Chichester, passing through 

 790 feet of Chalk, from top to bottom : and we also knew that at 

 Southampton there was a greater thickness, over 850 feet having 

 been passed through without reaching the bottom. The only 

 additional information gained is from the Warren Farm Well at 

 Telscombe, east of Brighton, which, starting from only a few feet 

 below the top, proves a thickness of nearly 960 feet. At the 

 outcrop in the Isle of Wight the thickness is much greater than 

 this ; and it seems therefore that, as in the London Basin, there is 

 some thinning towards the middle ; but it is unsafe to generalize 

 much from such scanty evidence. 



While at Chichester a thickness of over 80 feet of Upper Green- 

 sand was found, without reaching the base, at Telscombe there are 

 but 10 feet of this division, and in this latter place alone (except in 

 parts outside the Chalk-escarpment) has the Gault been reached. 

 It has, however, been pierced to the base, giving the high thickness 

 of 312 feet and being apparently underlain by Lower Greensand. 



Along the border of the Chalk in Eastern Sussex it has been proved 

 that the Gault is much thicker than had been thought, ranging up 

 to more than 300 feet indeed, in one case 345, or a trifle more 

 than at Caterham. It has also been found that the Lower Green- 

 sand is very thin and sometimes absent, the Gault then resting 

 on Weald Clay. 



Except, therefore, in the neighbourhood of the outcrops of the 



