330 THE REVOLUTIONS OF THE CRUST OF THE EARTH. 



those of Egypt. If we also take into account the fossil remains found 

 in the bone-caves of Sicily, we must admit, with M. Anca, that Europe 

 was connected with the African continent by two isthmuses ; the one 

 represented by the present submerged plateau, which extends from the 

 southern point of Sicily to Africa ; the other, easier to determine, is the 

 isthmus of the columns of Hercules, which united Morocco with Spain. 

 All these facts show us the dependence which exists between the 

 organic and inorganic world. If the exterior conditions influence the 

 dev^elopraentand the distribution of plants and of animals, on the other 

 hand animals and plants modify the structure of the sedimentary rocks, 

 by depositing upon them their organized remains. But in general we 

 may say that the end toward which all the forces of nature tend is 

 found in organization of matter, and consequently the crowning act is 

 the formation of living creatures, animals endowed with sensation, and 

 lastly of man, the final expression of the creative force of the earth. 



CHAPTER V. 



ICE. 



From the appearance of the first organisms until our time, the earth 

 has experienced every degrea in the climatic scale, from the warm and 

 uniform to the rigor of later periods. Besides this slow cooling, it is 

 evident there were oscillations of temperature, from the periodic increase 

 and decrease in the extension of certain plants of the temperate re- 

 gions.* We still find, even in our day, in difl'erent parts of the globe, 

 changes of climate, the cause of which is far from evident. M. Charles 

 Zenger concludes, from his numerous observations, that the annual heat 

 of central Europe sensibly increases, but is not able to attribute this 

 change to any known cause.t His observations coincide with the ap- 

 pearance of meridional plants in the north of Germany, noticed in 1835- 

 183G. We may, on the contrary, attribute to a slow cooling the increased 

 extent of the Swiss glaciers, which, from the twelfth century, have more 

 and more obstructed the ancient passes of the mountains, destroying 

 forests and habitations and reducing the temperature of the surround- 

 ing country. In France and Belgium, the culture of the vine has ceased 

 in many regions, where formerly its products were of great importance. 

 The disappearance of pines in Ireland indicates that Great Britain also 

 experiences this decrease of temperature. But the most striking proof 

 of a considerable cooling is furnished us by the dwindling and decay of 

 the birch forests of Iceland. This island, eminently volcanic, was, in 

 the middle ages, the seat of an advanced civilization. The arts and 

 sciences flourished there, and its poetry still astonishes the reader by its 



* Count Gast. de Sporta, Annals and Magaz. of Natural History, 3(1 ser., vol. sis, 18(57, 

 p. 351. 



t Phil. Magaz., June, 1868, p. 433. 



