OCR Text |
Show OF VOLCANOS. 393 volcanic phenomena are probably the result of a communication either permanent or transient between the interior and exterior of the globe. Elastic vapours press the molten oxidizing substances upwards through deep fissures. Volcanos might thus be termed intermitting springs or fountains of earthy substances; i. e. of the fluid mixture of metals, alkalies, and earths which solidify into lava currents and flow softly and tranquilly, when being upheaved they find a passage by which to escape. In a similar manner the Ancients represented (according to Plato's Phredon) all volcanic fiery currents as streams flowing from the Pyriphlegethon. To these considerations and views let me be permitted to add another more bold. May we not find in this internal heat of our globe-(a heat indicated by thermometric experiments on the waters of springs rising from different depths (3) as well as by our observations on volcanos)-a cause which may explain one of the most wonderful phenomena with which the study of fossils has made us acquainted? Tropical forms of animals, and, in the vegetable kingdom, arborescent ferns, palms, and bambusacere, are found buried in the cold regions of the North. Everywhere, the Ancient World shows 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 favorable or unfavorable 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 oxidation, 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 |