Geological Socieiy. 213 



lowed me. The merit of Mr. Babbage's paper, as far as original ob- 

 servation is concerned, consists principally in his notice of various 

 stalactitical deposits, and his examination of their different charac- 

 ters and modes of production. 



Mr. Babbage describes in detail all the appearances of this tern- 

 pie, and then inquires into the causes of the extraordinary revolu- 

 tions which it must be admitted on all hands to have undergone : the 

 principal difficulty, you are aware, is to account for the erosion of the 

 columns by lithophagous animals, from the height of 11 feet to 19 

 above their base, the remaining parts being intact. 



Mr. Babbage is of opinion that the building stood at first very 

 nearly at its present level. Assuming that since that period it has 

 both subsided and risen again, and that considerable changes have 

 taken place in the relative levels of the land and sea in its vicinity, 

 he explains these circumstances by supposing the edifice to have 

 been built upon the surface of matter at a high temperature, which 

 matter contracted afterwards by slow cooling ; that at a still subse- 

 quent period a fresh accession of heat produced a new expansion, 

 and that in this way the temple was gradually restored to its ori- 

 ginal level. 



To suppose and illustrate his reasoning, the author has constructed 

 a Table (founded on experiments made in America,) showing in 

 feet and decimals what would be the amount of expansion in beds 

 of granite from 1 to 500 miles thick at various temperatures ; toge- 

 ther with a formula for calculating the amount of expansion in si- 

 milar volumes of marble and sandstone j this Table has a collateral 

 claim to notice, as being the first worked out by the calculating en- 

 gine with a view to publication. 



It appears to me, that in applying the calculation, it is very ne- 

 cessary to take into account three elements which have been over- 

 looked. 



1. How far under the supposed conditions expansion would be 

 counteracted by pressure? 



2. What space of time would be required to heat or cool such 

 enormous masses of substances, which are very imperfect conductors 

 of caloric, to the required temperatures*? 



3. How far the explanation given of the phenomena of the Sera- 

 peum is applicable to others in its vicinity? The admitted fact that 

 certain buildings which have also subsided still remain below the 

 level of the sea, while others have been raised to unequal heights 

 above it, makes it unlikely that any uniform cause, while it produced 



* On a statement of Mr. Scrope's, that a current of lava after it had been 

 ejected nine months, was still flowing on the flanks of Etna at the rate of a 

 yard per day, Mr. de la Beche observes, " If lava can retain its elevated 

 " temperature when thus exposed, what length of time may we not allow for 

 " its doing so within the pipe of the volcano itself, surrounded on all sides by 

 " matter greatly heated, and like itself an exceedingly bad conductor of heat? 

 " Even in those cases where centuries elapse between the great eruptions 

 " of any given volcano, the lava is probably liquid beneath at no very con- 

 " siderable depth." 



