576 Geological Society. 



tion is another depression of 5 feet, the upper part of the fissure being; 

 filled with chalk rubble, sand and flint, and the bottom hollowed into 

 a cave 10 feet high, and from 15 to 20 feet deep. At 10 yards from 

 this point the flint layer dips beneath the beach. The chalk clilF 

 continues for about 800 paces further, gradually decreasing in alti- 

 tude, but capped by sandy loam and chalk rubble. Beyond this point, 

 the tertiary strata commence, consisting, in the upper part, of 7 to 18 

 feet of sand and sandy clay, with occasional masses of sandstone and 

 layers of shells ; and in the lower part of 7 feet of bluish clay, which 

 also incloses shells. These strata are visible for about 570 yards, 

 and then dip beneath the marshes. Mr. Morris considers them the 

 equivalents of the beds between Reculver and Heme Bay, agreeing 

 in position, mineral characters, and organic remains. They are 

 overlaid by the same superficial detritus as the chalk. 



The destruction of the cliff^s is calculated to have been, until 

 means were taken to defend them, at the rate of 3 feet annually. At 

 the cove before-mentioned, the sea removed in 25 years, about 20* 

 yards, including two cottages and a garden. 



The wells at the Preventive Station and Pegwell, are sunk 

 about 30 feet, through loam and chalk. The water is 10 feet deep, 

 but it is sometimes brackish, being aff^ected by the rise and fall of 

 the tide. It is generally lowest after the tide has flowed one hour, 

 and remains in that state about two hours, after which it rises. 

 Whether this effect is connected with the faults in the cliffs, Mr. 

 Morris doubts ; but he states, that a freshwater spring issues from 

 the beach at low water, opposite the well at the Preventive Station. 



Jan. 31. — An extract was first read from a letter addressed by Sir 

 John Herschel to Mr. Lyell, and dated Feldhausen, June 12, 1837. 



In former letters addressed to Mr. Lyell and Mr. Murchison, dated 

 Feldhausen, Feb. 20, and Nov. 15, 1836, and read before the Society 

 May 17, 1837*, Sir John Herschel first proposed his theory relative 

 to the increment of temperature from below, which would be pro- 

 duced in certain portions of the earth's crust by the partial distribu- 

 tion of additional sedimentary matter over the bottom of the ocean ; 

 and of the effects which would naturally result from this operation, pro- 

 ducing the phsenomena of earthquakes, and elevation and depression of 

 strata. In this letter he states, he was not then aware that Mr. Babbage 

 " had speculated on that peculiar mutual re -action of the surface and 

 the interior of the globe, and which must be called the secular vari- 

 ation of the isothermal surfaces of the latter ;" nor was he aware of 

 the notice in the Proceedings! of Mr. Babbage's paper on the Temple 

 of Serapis, until his attention was recently called to it by Mr. Lyell 

 and Mr. Murchison, but at the end of which notice a theory iden- 

 tical in the leading point is given. 



With respect to the first development of the theory, Sir John 

 Herschel says, ** the employment of the pyrometric expansion of 



* Proceedings of Geol. Soc. vol. ii. p. 548. [Or Lend, and Edinb. Phil. 

 Mag. vol. xi. p. 212, 214.] 



t Proceedings, vol. ii. p. 72. [Or Lond. and Edinb. Phil Mag. vol. v. 

 p. 213.] 



