I06 JOURNAL OF SCIENCE. 



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a place for the glacial period ; but this theory, if true, must provide for 

 alternation of warm and cold periods at the poles throughout all geo- 

 logical time. Professor James Geikie of Scotland, in his ' Great Ice 

 Age,' indorses this theory, and attempts to find evidences of former 

 glacial action, not only in the tertiary, but also in mesozoic and 

 paleozoic times. But the weight of the evidence seems to be against 

 this theory, and Mr. Geikie himself admits that that much of his 

 'evidence ' is ' not very convincing.' 



"The best and most satisfactory explanation of the warm and cold 

 periods at the poles has been made by Professor C. B. Warring, in a 

 paper read by him before the New York Academy of Science, and pub- 

 lished in the Popular Science Monthly for July, 1886. This paper 

 merits a much more extended notice than it has apparently received, for 

 its author has very strongly fortified his several propositions. Briefly, 

 his argument is this : The existence of tropical vegetables in Arctic 

 latitudes cannot be supported upon the theory of a warm tempera- 

 ture only. Light was as necessary as heat ; and this light must also 

 have been uniform and unbroken by long periods of darkness, for if 

 there had been a long night of four months in every year, as now, it 

 would have been fatal to all plants, and even many or most of the 

 animals. Therefore, down to nearly the close of the tertiary, the axis 

 of the earth was perpendicular to the ecliptic, and the days and nights 

 were everywhere and always equal. The temperature was kept up by 

 means of the carbonic acid and aqueous vapor in the atmosphere, which 

 formed a sort of 'double blanket,' and served to retain the heat radiated 

 from the sun. After a long period the carbonic acid was most of it 

 taken up from the atmosphere to form our coal-beds, peat, petroleum, 

 graphite, etc. This process was followed by a thinning of the retaining 

 cover. The heat from the sun was not all retained, but was lost again 

 by escaping into stellar space. 'Holes in the blanket' appeared at the 

 poles, ice and snow began to accumulate there, and eventually the 

 glacial epoch was inaugurated. Furthermore, he shows, that, according 

 to the nebular hypothesis, the axes of the earth and moon ought to have 

 been, in their normal condition, parallel with each other, and both 

 perpendicular to the plane of the ecliptic ; but instead, the earth's axis 

 is inclined 23|°, while the moon's axis is practically perpendicular, it 

 being inclined only 1° 30'. The change, therefore, was with that of the 

 earth, and was effected since the moon's separation from the earth. 'In 

 view of all these facts,' he says, ' it seems most probable that in that 

 blank interval the glacial epoch s or more largely between the end of the 

 miocene and the beginning of the Champlain, that movement occurred 

 which gave the earth seasons, imequal days and nights, and greatly 

 enlarged its limits of inhabitability. . . . When the axis became 

 oblique, more solar heat fell within the polar circle, these regions became 

 warmer, and the glacial epoch departed. If these conditions — a perpen- 

 dicular axis and high uplifts — could be to-day restored, the atmosphere 

 remaining as it is, the glacial epoch would return.' 



" It is the purpose of the present article to emphasise the reasons 

 for believing the direction of the earth's axis was changed about the 

 time stated above, and also to suggest the probable cause of the change. 

 In order to do this more intelligently, we must take a more comprehen- 



