Geological Society, 2 1 5 



10 feet ; — a line of perforations by Modiolae is visible in a cliff op- 

 posite the island of Nisida, 32 feet above the present level of the 

 Mediterranean. 



The author considers the preceding inferences as a legitimate 

 induction from the observed and recorded facts; and proceeds 

 to suggest an explanation of the gradual sinking and subsequent 

 elevation of the ground on which the temple stands. From some 

 experiments of Col. Totten, recorded in Silliman's Journal, he has 

 calculated a table of the expansion, in feet and decimal parts, of 

 granite, marble, and sandstone, of various thicknesses, from 1 to 

 500 miles, and produced by variations of temperature of 1°, 20°, 

 50°, 100°, 500° of Fahrenheit : and he finds from this table, that if 

 the strata below the temple expand equally with sandstone, and 

 a thickness of five miles were to receive an accession of heat 

 equal only to 100°, the temple would be raised 25 feet;— a greater 

 alteration of level than is required to account for the phenomena 

 in question. An additional temperature of 50° would produce the 

 same effect upon a thickness often miles; and an addition of 500° 

 would produce it on a bed only a single mile in thickness. 



Mr. Babbage then adverts to the various sources of volcanic 

 heat in the immediate neighbourhood : and he conceives that the 

 change of level may be accounted for by supposing the temple to 

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

 which subsequently contracted by slowly cooling down ; — that when 

 this contraction had reached a certain point, a fresh accession of 

 heat from some neighbouring volcano, by raising the temperature 

 of the beds again, produced a renewed expansion, and which re- 

 stored the temple to its present level. The periods at which these 

 events happened are then compared with various historic records. 



The second part of this letter contains some views, respecting 

 the possible action of existing causes, in elevating continents and 

 mountain-ranges, which occurred to the author in reflecting on 

 the preceding explanation. He assumes as the basis of this rea- 

 soning the following established facts: 



1. That as we descend below the surface of the earth at any 

 point, the temperature increases. 



2. That solid rocks expand by being heated j but that clay 

 and some other substances contract under the same circumstance. 



3. That different rocks and strata conduct heat differently. 



4. That the earth radiates heat differently, or at different parts of 

 its surface, according as it is covered with forests, with mountains, 

 with deserts, or with water. 



5. That existing atmospheric agents and other causes, are con- 

 stantly changing the condition of the surface of the globe. 



Mr. Babbage then proceeds to remark, that whenever a sea or 

 lake is filled up, by the continual wearing down of the adjacent 

 lands, new beds of matter, conducting heat much less quickly than 

 water carries it, are formed ; and that the radiation, also, from the 

 surface of the new land, will be different from that from the water. 

 Hence, any source of heat, whether partial or central, which pre- 



