cii GENERAL SUMMARY OF SCIENTIFIC AND 



former geological periods. We have there no clear evidence with 

 regard to the Silurian and Devonian ages ; but in the Carboniferous 

 time there was an extensive continental area around the pole, sup- 

 porting a colossal vegetation, the remains of which, inclosed in sand- 

 stones, rest in Spitzbergen upon a great formation of marine lime- 

 stone rich in corals of Carboniferous age. The Trias of this region 

 shows gigantic cephalopods and great saurians, which also point to 

 a tropical climate, and the succeeding Jurassic in Spitzbergen is ter- 

 restrial, with large cycads and conifers. The Cretaceous of the polar 

 regions also, according to this same observer, shows two horizons a 

 lower one, with a flora which Heer compares to that of Egypt, and 

 an upper, which contains a great variety of deciduous trees, and in- 

 dicates, for the first time, a slight change of climate. The Eocene 

 is wanting in these regions; but we have the wonderful Miocene 

 flora, which was spread over a great arctic continental area, and is 

 well known to have resembled that of Central Europe, or of the Ohio 

 valley of to-day. 



FORMER ARCTIC CLIMATE. 



Nordenskjold, moreover, fails to find evidences of former glacial 

 agencies in the sandstones of these regions from which we might in- 

 fer the former existence of alternations of warm and cold climates. 

 The advent of frost followed the Miocene period. Recent sjDecula- 

 tions liave revived the old notion of a possible change of the earth's 

 axis of rotation as a way of explaining this change of arctic climate ; 

 but such a phenomenon is astronomically improbable, and is also op- 

 posed by the fact that the direction of oceanic currents, which are 

 guided by the earth's rotation, appears, from the distribution of ma- 

 rine sediments, to have been the same since very early periods. Some- 

 thing may have been due to the depression of parts of the present 

 continents, which may have permitted the influx of warm waters into 

 arctic seas, but the evidence shows the existence of arctic continental 

 areas charged with vegetation. A simple solution of the problem 

 seems to be that long since proposed by the present writer, that the 

 presence of a larger amount of carbonic acid in the atmosphere up 

 to a late period, maintained, in accordance with well-ascertained 

 physical laws, a tropical temperature over the whole earth's surface, 



at the sea-level. 



ANTARCTIC CLIMATE. 



In this connection may be noted the question of a glacial period 

 in the southern hemisphere. McCoy, from his studies of the fossil 

 forms of Southern Australia, concludes that there is no evidence 

 of a former period of greater cold, but that there has been a gradual 

 diminution of temperature down to the present time. Hutton shows 

 that the evidence in New Zealand is to the same efiect, as Hector 

 had already done before him. 



