110 Mr Charlesworth on the Age 



forms sulphates. In this manner various products are produced, 

 which accumulate at the edges of the gas springs. 



As the rocky hill, on whose declivity the gas springs are 

 scattered, consists of loose tuffas and slags, and since the acid 

 vapours penetrate the mass in all directions by innumerable 

 canals, it is not surprizing that we should find the rock com- 

 pletely decomposed, so far at least as the gas springs extend. 

 It is difficult to find a fragment of slag, which has not been 

 converted into a brittle and soft mass of clay. The ground 

 consists of a soft clay, rendered moist by the watery vapours, 

 and presenting yellow, red, blue, or other tints of colour. The 

 water of the lower gas springs is mixed with these clays, and in 

 this way acquires its varied colours. 



Round each gas spring, there is a small rim of alternating 

 layers of clay and sulphur, to which are occasionally added 

 some sulphates : as gypsum, alum, and sulphate of iron. The 

 temperature of the evolved gases is always very high. It even 

 sometimes exceeds the boiling heat of water. The surface of 

 the ground is so hot, that one can hardly touch it with the 

 hand. 



(To be concluded in our next.} 



On some Fallacies involved in the Results relating to the Com- 

 parative Age of Tertiary Deposits, obtained from the Applica- 

 tion of the Test recently introduced by Mr Ly ell and M. Des- 

 hayes.* By EDWARD CHARLESWORTH, Esq., F. G. S. 

 DURING the author's investigation of the fossiliferous strata 

 above the London clay in Suffolk and Norfolk, some facts have 

 come under his observation, which appear to him to point out 

 sources of error to a considerable extent in the application of 

 the test recently proposed by M. Deshayes and Mr Lyell, and 

 which is now so generally made use of in the classification of ter- 

 tiary formations. 



The crag has been referred by Mr Lyell to his older pliocene 

 or upper tertiary period, on the authority of Deshayes, who 

 identified among the fossil testacea of that deposit, 40 per cent. 



* The above is an abstract of the memoir read before the Members of the 

 British Association, at Bristol, August 26. 1836. 



