experiments on the waters of springs rising from different depths,[3] as well by our observations on volcanos),—a cause which may explain one of the most wonderful phænomena with which the study of fosssils has made us acquainted? Tropical forms of animals, and, in the vegetable kingdom, arborescent ferns, palms, and bambusaceæ, are found buried in the cold regions of the North. Everywhere the ancient world shews a distribution of organic forms at variance with our present climates. To resolve so important a problem, recourse has been had to several hypotheses; such as the approach of a comet, a change in the obliquity of the Ecliptic, and a different degree of intensity in the solar light. None of these explanations are satisfactory at once to the astronomer, the physicist, and the geologist. For my part I willingly leave the axis of the Earth in its place, and suppose no change in the light of the solar disk (from whose spots a celebrated astronomer was inclined to explain the favourable or unfavourable harvests of particular years); I am disposed to recognise that in each planet there exist, independently of its relations to the central body of the system to which it belongs, and independently of its astronomical position, various causes for the development of heat;—processes of oxydation, precipitations and chemical changes in the capacity of bodies, by increase of electro-*magnetic intensity, and communications opened between the internal and external portions of the planet.
It may be that in the Ancient World, exhalations of heat issuing forth through the many openings of the deeply
