THE 



EDINBURGH NEW 



PHILOSOPHICAL JOURNAL. 



On the Palceohydrography and Orography of the Earth's 

 Surface, or the probable pos Ition of Waters and Continents, 

 as well as the probable Depths of Seas, and the absolute 

 Heights of the Continents and their Mountain- Chains du- 

 ring the different geological periods. By M. Ami Boue'. 

 Communicated by the Author. 



(Continued from vol. lv., page 316.) 



But we give the means to determine approximative^ this 

 value by another way, so that it is possible to control this geo- 

 gnostic bathographic mode of determination by the more geo- 

 detic one. Another control is given us by the estimation made 

 by Humboldt for the maximum of the medium of continental 

 heights, and the height of the point of gravity in the volume 

 of all continents above the present level of the sea. He was 

 led to this by the evident errors of Laplace, who estimated 

 4000 feet the middle elevation of continents. Humboldt 

 found 157*8 toises, or 307 metres, or 942 feet, for this value, 

 but he left out of consideration and calculation the whole of 

 Africa, where there exist immense plains, as well as very 

 extensive plateaux, and even in the south-east very high and 

 extensive chains. Nor could he have had, during the time of 

 his calculation, an exact idea of the greatness and altitude of 

 the lofty plateaux and plains of North America ; and he 

 must have overlooked also all what is called the polar 

 countries or islands, where high chains are not uncommon, 

 especially at the Austral pole. For that reason A. K. John- 

 ston differs already a little from Humboldt; for he admits 



VOL. LVI. NO. CXI, — JANUARY 1854. A 



