PHYSICAL GEOGRAPHY. 301 



the surface of France, only raise its mean level about 115 

 feet. The mass of the eastern and western Alps would in 

 like manner only increase the height of Europe about 21|^ 

 feet above its present level. I have found by a laborious in- 

 vestigation,* which, from its nature, can only give a maximum 

 limit, that the center of gravity of the volume of the land 

 raised above the present level of the sea in Europe and North 

 America is respectively situated at an elevation of 671 and 

 748 feet, while it is at 1132 and 1152 feet in Asia and South 

 America. These numbers show the low level of northern 

 regions. In Asia the vast steppes of Siberia are compensated 

 for by the great elevations of the land (between the Himalaya, 

 the North Thibetian chain of Kuen-lun, and the Celestial 

 Mountains), from 28° 30' to 40^ north latitude. We may, 

 to a certain extent, trace in these numbers the portions of the 

 Earth in which the Plutonic forces were most intensely mani- 

 fested in the interior by the upheaval of continental masses. 



There are no reasons why these Plutonic forces may not, 

 in future ages, add new mountain systems to those which Elie 

 de Beaumont has shown to be of such different ages, and in- 

 clined in such difierent directions. Why should the crust of 

 the Earth have lost its property of being elevated in ridges ? 

 The recently-elevated mountain systems of the xllps and the 

 Cordilleras exhibit in Mont Blanc and Monte Rosa, in Sorata, 

 Illimani, and Chimborazo, colossal elevations which do not 

 favor the assumption of a decrease in the intensity of the sub- 

 terranean forces. All geognostic phenomena indicate the 

 periodic alternation of activity and repose ;t but the quiet 

 we now enjoy is only apparent. The tremblings which still 

 agitate the surface under all latitudes, and in every species of 

 rock, the elevation of Sweden, the appearance of new islands 

 of eruption, are all conclusive as to the unquiet condition of 

 our planet. 



* De la hauteur Moyenne des Conlments, in my Asie Centrale, t. i., p. 

 82-90, 165-189. The results which I have obtained are to be regard- 

 ed as the extreme value {nombres-limites). Laplace's estinuile of the 

 meau height of continents at 3280 feet is at least three times too high. 

 The immortal author of the Mecanique Celeste (t. v., p. 14) \va.s led to 

 this conclusion by hypothetical views as to the meau depth of the se:i. 

 I have shown (Asie Centr., t. i., p. 93) that the old Alexandii;iu math- 

 ematicians, on the testimony of Plutarch {in JEmilio Paulo, cap. 1.5), 

 believed this depth to depend on the height of the mountains. Tlie 

 height of the center of gravity of the volume of the continental masses 

 is probably subject to slight variations in the course of many c.'!ntu:ie.s 



t Zioeiier Geologischer Brief von Elie de Beaumont an Alexander von 

 Humboldt, in Poggendorf'.s Annalen, bd. xxv., s. 1-58. 



