REFRIGERATION OF THE GLOBE. Since the mathematical researches of Fourier regarding the diffusion and conduction of heat In a mass constituted as the earth appears to be in the parts near the surface, hare become in some degree known, geologists have been much encouraged In attempting to connect with a gradual change and diminution of the internal temperature of the globe, such as would be consistent with Fourier's theoretical results, the higher order of geological inferences. The phenomena of a general if not universal base of once melted rocks below all the strata, the peculiar (often called metamorphic) condition of the lowest of these as compared with the upper, the absence or rarity of fossils in the lowest strata, the evidence of even general high surface temperatures on the ancient land and in the ancient sea as contrasted with the modern distribution of climates, are all consequences supposed to be derivable from the assumption of the earth having once been thoroughly very hot, and being now partially cooled by radiation of heat into the cold planetary and stellar spaces around ne. But though such a deduction of pheno• mena from a primal condition of our planet is or appears to be correct enough to justify geologists in employing the hypothesis as a means of discovering truth, they must be careful neither to disregard inquiries into the certainty of the fundamental assumption, nor to neglect a scrupulous examination of its consequences.
On the first point Professor Whewell communicated to the Geo logical Section of the British Association at Dublin (1835), some observations which are likely to be influential on the second point, and which can neither be condensed nor amended.
" The heat of the interior parts of the earth has always been treated of by those who have established the theory of heat upon mathematical principles. They have hitherto considered it as proved upon such principles, that the increase of temperature of the substance of the earth as we descend proves the reality of an original heat. But M. Poisson, in his Theerie de Is Chaleur,' just published, dissents from this opinion, and is disposed to assign another reason for the higher temperature below the surface. He observes that the cosmical regions in which the solar system moves have a proper temperature of their own ; that this temperature may be different in different parts of the universe; and that, if this be so, the earth would be some time in acquiring the temperature of the part of space in which it has arrived. This temperature will be propagated generally from the surface to the interior parts. And hence, if the solar system moves out of a hotter into a colder region of space, the part of the earth below the surface will exhibit traces of that higher temperature which it had before acquired. And this would by no means imply that the Increase of temperature goes on all the way to the centre." (' Report of the British Association for 1835; p. 66.) A speculation, perhaps in reality involving such views as those of 31. Poisson, though founded on examinations and inferences among the Helvetia Alpe, was subsequently brought prominently before the geological world by M. Agassiz. According to this very distinguished naturalist, there is evidence from the peculiar effects left by glaciers, in the valleys of Switzerland and on the surface of the Jura Mountains, that the icy mantle which now wraps the High Alps once filled the valleys for miles beyond its present limits, and, consequently, that the blocks of Mont Blanc and the Valoraine were carried across the Lake of Geneva to the Jura, by a mere glacier movement across an ice-filled hollow. Dr. Buckland and Mr. Lyell have endeavoured by similar
evidence and reasoning, by the evidence of scratched, smoothed and grooved surfaces of rock, and the appearance of moraine heaps in the Highlands of Scotland, near Edinburgh, and in Cumberland and Westmoreland, to prove that glaciers anciently covered large tracts of the Caledonian and Cumbrian regions. (' GeoL Proceedings,' 1840, November and December.) Moreover, It is understood to be the opinion of M. Agana: that the icy covering thus attempted to be demonstrated by its remaining effects in the mountainous parts of Great Britain, "once extended over all the north of Europe and the north of Asia and America," and that in this" mass of ice the elephants and other mammalia found in the frozen mud and gravel of the arctic regions were imbedded at the time of their destruction." To the quick melting of this immense mass of ice and the currents of water which resulted, the author attributes the transport and deposition of the "masses of irregularly rounded boulders and gravel which fill the bottom of the valleys, innnmerable boulders having at the same time been transported, together with mud and gravel, upon tho masses of the glaciers then set afloat" (See the work of M. Agassiz, entitled ' Etudes eur les Glaciers de Is Suisse,' and the accounts of his observations before the British Association at Glasgow in 1840.) Now it is obvious that in examining this speculation, two ways are open : first, a careful comparison of the phenomena with the hypo thesis which is proposed for their explanation ; secondly, an Inquiry into the probability of the conditions which might render such a general and extreme refrigeration of the globe as the hypothesis requires possible. Confining our remarks to the former process, we may observe : first. that to admit the ancient existence of glaciers in some of the Highlands and Cumberland valleys which display glacial ejects, is one thing ; to admit glacial action as the physical cause of the dispersion of boulders and gravel, another. Glaciers are found at this day in corresponding latitudes and at corresponding elevations in the southern parts of America: a local effect of causes which may be con ceived to have formerly produced an equal effect in theasorthern zone : but the distribution of the boulders and gravel Is so peculiar and yet PO various, the dispersion of them so wide in regions where, according to the present configuration of the land, they could not be pushed by glaciers, nor carried by floating ice ; and the connection of these circumstances with a great change of organic life, so strict, that It is hardly conceivable auoh effects could be due to anything but a cause simultaneously general or successively repeated. Of the physical causes by which the explanatiou of this great phenomenon has been attempted, it will suffice to mention three : 1. Great and extensive oceanic action consequent eu mighty mis placements of the solid land, and corresponding changes of land and sea.