THE REVOLUTIONS OF THE CRUST OF THE EARTH. 353 



According to the estimate of M. Meech, the annual mean of heat 

 received by the polar zone and upon a surface taken as unity, is th« 454 

 thousandth part of the heat received upon the same surface at the 

 equator. As the quantity of heat transported by the Gulf Stream is 

 equivalent to the heat received by a surface of 659,344 square leagues 

 of the Antarctic regions, and as the surface of these regions is 830,000 

 square leagues, the amount of heat transported toward the polar regions 

 by the single oceanic current, is nearly as great as the heat received 

 directly from the sun by all the glacial zone. The quantity of heat 

 transported by the current is to the quantity of direct heat as 15 is to 

 18. The two quantities are completely equalized, if we take into account 

 the absorption of heat in the atmosphere, which ought to be greater 

 because of the obliquity of incidence. 



The Gulf Stream does not transfer all its heat to the poles ; it yields 

 up a certain quantity in the temperate regions ; but, on the other hand, 

 this current is not the only one, and the combined action of all the 

 oceanic currents united to that of the atmospheric currents, can con- 

 siderably augment the action of the eccentricity and obliquity of the 

 orbit and free the poles, at certain periods, of the ice which covers 

 them. When the obliquity of the ecliptic was at the maximum and an 

 eighteenth more of direct heat fell upon the poles, the effect was to 

 modify the severity of the cold of the hemisphere under ice, and to fa- 

 cilitate on the other hand the melting of the snow upon the hemisphere 

 which enjoyed a uniform climate. If a great obliquity coincided with 

 the other cosmic causes which diversify the climates of the two hemis- 

 pheres, their co-operation could produce these exceptional conditions of 

 temperature, the influence of which upon the organic and inorganic 

 world of different periods is well established. 



COi^CLUSION. 



MAN. 



Science can find no particular circumstance which has marked the 

 appearance of man ; nor can she more definitely fix the period when 

 this king of creation, a title humanity is pleased to assume, entered 

 into the possession of his domain. It has sometimes been supposed 

 that certain great changes in the conditions of existence which were 

 fatal to a great number of mammalia, at the same time prepared the 

 conditions for the appearance of the human race. 



For a long time it was a disputed question whether man preceded the 

 later glacial phenomena ; that is, if he might be found in the fossil state. 

 Cuvier positively denied this; he would not admit that man was con- 

 temporary with the great mammals of the Quaternary period, and all 

 his school, strong in the authority of their master, refused for a long 

 time to accept opposing, although well-established, testimony. 



Archseology prepared the way for the solution of this grave problem 

 s 23 



