THE REVOLUTIONS OF THE CRUST OF THE EARTH. 331 



freshness and vivacity. But then, as numerous documents testify, all 

 nature contributed to enlarge the ideas and excite the imagination of 

 the poet. The magnificent woods were peopled with numerous animals, 

 and the nightiugale made music in the groves of this island now ravaged 

 by cold and fire. Spitsbergen, formerly accessible, is now completely 

 surrounded by ice. Greenland, once a flourishing colony, founded in 

 982 by the I^orwegians, commenced to decline about 1348, and this 

 verdant country, which, according to a list found in Eome, had already, 

 anterior to the fourteenth century, seventeen bishops, and numerous 

 relations with Iceland and Norway, had to be discovered anew in the 

 sixteenth century. Today it is completely covered with ice, and its 

 eastern side is altogether uninhabitable.* 



It is also a well known fact that the passage between the Pacific and 

 the Atlantic oceans, by the polar sea, is becoming more and more im- 

 practicable and even impossible, on account of the ice which obstructs 

 the straits and canals. 



We cannot say with Boussingault that to an elevation of the mountain- 

 chain of the Andes must be attributed the retreat of the line of per- 

 petual snow, for a change of climatic conditions in the general direction 

 of the winds, and the quantity of airaospheric precipitations takes 

 place more readily in certain regions, and may consequently modify the 

 climate. 



If we pass from the local to the general distribution of climates over 

 the globe we are struck with the unequal division of heat in the two 

 hemispheres. The borders of the southern glacier attain, and sometimes 

 pass beyond, the seventy-fifth parallel, while the northern glacier reaches 

 very nearly the eightieth parallel. Travelers who have wintered on the 

 borders of the southern glacier have shown us, by means of thermometric 

 tables, that the mean temperature is hardly higher than that of northern 

 latitudes very near the pole, in which some vessels have been forced to 

 remain during the winter season. Dumont d'Urville affirms that the 

 floating islands of ice frequently encountered in the southern sea are of 

 a size unknown among the icebergs of the northern hemisphere. Their 

 length exceeds sometimes 20 kilometers (12J miles), and their height 30 

 meters (98 feet). This enormous mass represents moreover only that 

 part of the ice which is above the surface of the water, and is only an 

 eighth of the entire amount.t 



Geological periods also give us proof of numerous oscillations of tem- 

 perature. In fact, after the Carboniferous period, so rich in vegetable 

 forms, we observe a relaxation and very marked diminution in the evo- 

 lution of animal and vegetable life during the Permian i)eriod and also 

 during a part of the Triassic period.| It is in the Permian deposit that 



*H. G. Bronn, Eandbuch einer GescMchte der Natur, t. i, p 131. Alpli. Favrc, iJec/ier- 

 ches geologiqucs, t. i, p. 178, note 1. 



tLyell, Travels in North America, 1845, vol. II, p. 100. 

 t D'Arcliiac, Cours de Paleont. Strat, t. ii, p. 11. 



