Another hypothesis connected with Laplace’s brilliant astronomical theory must be added, in order to describe the formation of the planetary crust. When the gaseous ring became condensed into a globe, it would not cease to contract, owing to the continued radiation of its caloric. The whole mass, having become liquid through the gradual cooling of its molecules, would be changed into a sea of lava whirling round in space; but this state was only one of transition. After an indefinite term of centuries, the loss of heat was sufficient to cause the formation of a light _scoria_, like a thin sheet of ice over the surface of the fiery sea, perhaps just at one of the poles where nowadays the extreme cold produces icebergs and a frost-bound sea. This first _scoria_ was succeeded by a second, and then by others; next they would unite into continents floating on the surface of the lava, and, finally, would cover the whole circumference of the planet with a continuous layer. A thin but solid crust would then have imprisoned within it an immense burning sea. This crust was frequently broken through by the lava boiling beneath it, and then, by means of the solidification of the _scoriæ_, was again united; the cooling process would tend also to slowly thicken it. After a lapse of time, which must have been immensely protracted--since the interval during which the temperature of the terrestrial crust would be lowered from 2,000° to 200° has been estimated, at the very least, at three and a half millions of centuries--the pellicle at last became firm, and the eruptions of the liquid mass within ceased to be a general phenomenon, localizing themselves at those points where the firm crust was the thinnest. The surrounding atmosphere, replete with vapors and various substances maintained by the extreme heat in a gaseous state, would gradually get rid of its burden; all kinds of matter, one after the other, would become disengaged from the luminous and burning aerial mass, and precipitate themselves on the solid crust of the planet. When the temperature was lowered sufficiently to enable them to pass from a gaseous to a liquid state, metals and other substances would fall down in a fiery rain on the terrestrial lava. Next, the steam, confined entirely to higher regions of the gaseous mass, would be condensed into an immense layer of clouds, incessantly furrowed by lightning. Drops of water, the commencement of the atmospheric ocean, would begin to fall down toward the ground, but only to volatilize on their way and again ascend. Finally these little drops reached the surface of the terrestrial _scoria_, the temperature of the water much exceeding 100°, owing to the enormous pressure exercised by the heavy air of these ages; and the first pool, the rudiment of a great sea, was collected in some fissure of the lava. This pool was constantly increased by fresh falls of water, and ultimately surrounded nearly the whole of the terrestrial crust with a liquid