The following explanation of the origin of many of the changes at present going on on the earth's surface, was suggested in endeavouring to account for the very singular phenomena presented by the temple of Jupiter Serapis, at Puzzuoli, near Naples. The facts relating to that temple were stated in a paper presented to the Geological Society of London, in March, 1834; an abstract of which was published shortly after.

The following positions are taken as the basis of the reasoning on this subject:—

1. That, as we descend below the surface of the earth, the temperature increases.

2. That solid rocks expand by being heated; but that clay, and some other substances, contract under the same circumstances.

3. That different rocks and strata conduct heat differently.

4. That the earth radiates heat differently, 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 constantly changing the condition of the surface of the globe.

The only one of these propositions on which, in the present state of knowledge, the slightest question can be raised, is the first. But the observations on which it depends have latterly become so numerous, that the general fact of an increase of temperature, on descending into the crust of the earth, can scarcely be questioned; although the exact law of this increase, and the extent to which it penetrates, are yet undecided.