z 3 6 THE POPULAR SCIENCE MONTHLY. 



The exhaustion of all other means of solution, joined to the masg 

 of positive evidence accumulated by recent science, throws us more 

 and more conclusively upon the idea to which Sir Charles Lyell has 

 firmly held from the first, and which may be taken as the culminating 

 point of his latest achievements in geology, that the predominant cause 

 of the great changes in climate is to be found in the distribution and 

 elevation of the land. The Glacial period may be traced to an exces- 

 sive and abnormal accumulation of land around the Pole. There is 

 absolutely no limit to the alternations which the surface of our globe 

 may have, or indeed has gone through. There is hardly a spot of what 

 is now land which has not been covered by the sea, probably not a 

 space now covered by the ocean which has not been at some time, if not 

 many times, dry land. In one epoch the land may have been chiefly 

 equatorial, at another polar or circumpolar. At "present we may readily 

 divide the globe into two equal parts, the land hemisphere and the wa- 

 ter hemisphere ; the former of which exhibits almost as much land aa 

 water, or as 1 to 1.106 ; while in the latter the proportion of land to 

 water, as made out by Mr. Trelawny Saunders, is only as 1 to 7.988. 

 The general proportion of land to sea may be taken throughout the 

 globe as 1 to 1\. Were the land, by the action of subterranean forces, 

 its total amount being unchanged, now gathered together in masses 

 along the equator and around the Poles alternately, such geographical 

 changes would amply suffice, as Sir C. Lyell makes it his task to show, 

 to explain the utmost vicissitudes which the climate of the earth has 

 undergone. This course of reasoning by no means precludes such aid 

 as may be brought in by independent verce causce, by the concurrence 

 of the cold period induced by excessive piling of land around the Pole 

 with wintering in aphelion, or at a period when the earth's axis was 

 abnormally inclined. These causes, especially in combination, would 

 greatly intensify what, after all, must remain the ruling and inherent 

 principle of climatic revolutions. We have only to look at the present 

 aspect of Greenland to satisfy ourselves what might become the state 

 of the British Isles by a mere substitution of other local conditions 

 under the same parallel of latitude. Were the Gulf Stream done away 

 with, the equatorial continents which now form vast reservoirs of heat 

 transferred to the Northern regions, and their snow-clad frozen surface 

 swept by Polar currents, how far south would the ice-sheet cover the 

 unsubmerged tracts of land, and the glaciers come down to the level 

 of the sea ? The chain of facts and reasonings by which Sir Charles- 

 Lyell binds together the phenomena which science and discovery con- 

 tribute to this intricate problem forms one of the most characteristic 

 features of his book. Every new link, and every additional degree of 

 tenacity given to his argument, enhances the value of this standard 

 work as a steadfast, clear-sighted, and consistent witness to the great 

 law of unifonnity and continuity in Nature. 



The latest information acquired by deep-sea dredging has been 



