Geological Theory of Isothermal Surfaces.
During one portion of my residence at Naples my attention was concentrated upon what in my opinion is the most remarkable building upon the face of the earth, the Temple of Serapis, at Puzzuoli.63
63 In this inquiry I profited by the assistance of Mr. Head, now the Right Hon. Sir Edmund Head, Bart., K.C.B., late Governor-General of Canada. An abstract of my own observations was printed in the “Abstracts of Proceedings” of the Geological Society, vol. ii. p. 72. My friend’s historical views were printed in the “Transactions” of the Antiquarian Society.
It was obviously built at or above the level of the Mediterranean in order to profit by a hot spring which supplied its numerous baths. There is unmistakable evidence that it has subsided below the present level of the sea, at least twenty-five feet; that it must have remained there during many years; that it then rose gradually up, probably to its former level, and that during the last twenty years it has been again slowly subsiding.
The results of this survey led me in the following year to explain the various elevations and depressions of portions of the earth’s surface, at different periods of time, by a theory which I have called the theory of the earth’s isothermal surfaces.
I do not think the importance of that theory has been well understood by geologists, who are not always sufficiently acquainted with physical science. The late Sir Henry De la Beche perceived at an early period the great light those sciences might throw upon his own favourite pursuit, and {465} was himself always anxious to bring them to bear upon geology.
I am still more confirmed in my opinion of the importance of the “Theory of Isothermal Surfaces in Geology” from the fact that a few years afterwards my friend Sir John Herschel arrived independently at precisely the same theory. I have stated this at length in the notes to the “Ninth Bridgewater Treatise.”