Ol28 Attempt to determine the mean height of Continents. 



that their depth is less than the elevation of high mountains, 

 as the deposits from the waves, and the remains of marine 

 animals, must have tended, in the lapse of time, to fill up these 

 great cavities." 



Considering the profound and extensive knowledge which 

 the author of the Mtcanique Celeste possessed in the highest 

 degree, an assertion of this nature was the more striking, as 

 ho could not be ignorant that the most elevated plateau of 

 France, that from which the extinct volcanoes of Auvergne 

 have risen, does not rise, according to Ramond, to more than 

 1044 feet, and that the great Iberian plateau is not, according 

 to my own measurements, more than 2100 feet above the level 

 of the sea. Laplace has therefore fixed the upper limit at 

 1 000 metres, merely because he has considered the extent and 

 the mass of the elevations of mountains to be much greater than 

 they really are, inasmuch as he has confounded the height of 

 tlie insulated peaks or culminating points with the mean height 

 of the mountain ridges ; he has admitted much too low a 

 number for the depth of seas, because, in his time, data could 

 not be found on the subject, and he has thence inferred the 

 proportion of the extent of the surface (in square miles) in re- 

 gard to all continents, to the extent of the projection of the 

 surfaces covered by mountains. 



A very exact calculation has shewn that the mass of the 

 chain of the Andes, in South America, from where it leaves the 

 whole portion of the eastern plains of the pampas and forests, 

 regions whose surface is one-third larger than that of Europe, 

 does not rise above 486 feet. M. de Humboldt hence con- 

 cludes, " That the mean height of continental lands depends 

 much less on those chains or longitudinal ridges of little 

 breadth which traverse continents, and on their culminating 

 points or domes, which attract common observation, than on 

 t!>e general configuration of the difl^erent orders of plateaux and 

 their ascending series, and on those gently undulating plains 

 with alternating slopes, which have an influence, by their mass 

 and extent, on the position of a mean surface, that is to say, on 

 the height of a plain placed in such a manner that the sum of 

 its positive ordinates shall be equal to the sum of its negative 

 ordinates."" 



