234 proceedings of the geological society. [feb. 24, 



February 3, 1847, 



A paper * On the London Clay,' by Joseph Prestwich, Jun., Esq., 

 F.G.S., was read. 



[The publication of this paper is postponed by the author's desire, in order 

 that it may be printed together with another paper on the Bagshot sands 

 subsequently read.] 



February 24, 1847. 



John Craig, Esq., Glasgow, was elected a Fellow of the Society. 



The following communications were read : — 



1 . On recent Depressions in the Land. 

 By James Smith, Esq., of Jordan-hill, F.G.S. 



The human period may be subdivided into the present, or that in 

 which geological events are subjected to our own observation ; the 

 historical, or that in which they have been observed and recorded ; and 

 the antiquarian, in which, although we cannot assign a date to them, 

 we can prove from human remains or works of art that they must 

 have taken place since the earth was inhabited by man. 



Having recently observed proofs of movements of depression in 

 each of these periods, I proceed to notice them in their retrograde 

 order. 



When I visited Pozzuoli in 1819, the floor of the temple of Serapis 

 was dry, but I remarked that the channels cut across it for the pur- 

 pose of draining the waters of the thermal spring which rises within 

 its precincts were nearly filled with sea-water, with a sensible current 

 flowing inwards, or from the sea ; when I returned in 1845, I found 

 that the high-water mark stood at 28 inches above the pavement, 

 exhibiting a rise of about an inch yearly. 



As there is a rise and fall of tide of nearly 10 inches within the 

 building, and as I have no means of knowing the state of the tide at 

 my first visit, I cannot speak with certainty as to the exact change of 

 level which had taken place during the interval between my observa- 

 tions ; I am however satisfied that it could not be much more or less 

 than one inch yearly. 



Professor Forbes of Edinburgh visited the temple in 1826, and 

 Mr. Babbagein 1828 ; and as both of these gentlemen took notice of 

 the state of the tide, and have favoured me with the record of their 

 observations taken at the time, I am enabled to compare them with 

 my own, and find that the differences agree very nearly with what I 

 have above stated. 



Professor Forbes found the depth of water at full tide about 12 

 inches, which is 1 6 inches below my measurement made eighteen years 

 and a half afterwards. 



Mr. Babbage, who made a section of the building, has marked the 

 high-water level about 2 inches below the top of the plinth, or lowest 



