186 COSMOS. 



the fissures and chambers of the elevated volcano. These 

 waters perpetually produce a refrigeration in the strata 

 through which they run down. Without them the whole 

 of the doleritic and trachytic mountains would acquire, even 

 at times when no near eruption is foretold, a still higher 

 temperature in their interior, from the volcanic source, per- 

 petually in action, although perhaps not lying at the same 

 depth in all latitudes. Thus, in the varying struggle of the 

 causes of heat and cold, we have to assume a constant tide 

 of heat upward and downward in those places where conical 

 solid parts ascend into the atmosphere. 



As regards the area which they occupy, however, mount- 

 ains and elevated peaks form a very small phenomenon in 

 the relief formation of continents ; and, moreover, nearly 

 two thirds of the entire surface of the earth is sea-bottom 

 (according to the present state of geographical discovery in 

 the polar regions of both hemispheres, we may assume the 

 proportion of sea and land to be in the ratio of 8 : 3). This 

 is directly in contact with aqueous strata, which, being 

 slightly salt, and depositing themselves in accordance with 

 the maximum of their density (at 38 -9), possess an icy cold- 

 ness. Exact observations by Lenz and Du Petit-Thouars 

 have shown that within the tropics, where the temperature 

 of the surface of the ocean is 78-8 to 80'G, water of the 

 temperature of 3C*5 could be drawn up from a depth of 

 seven or eight hundred fathoms phenomena which prove 

 the existepce of under currents from the polar regions. The 

 consequences of this constant, sub-oceanic refrigeration of by 

 far the greater part of the crust of the earth deserve a degree 

 of attention which they have not hitherto received. Rocks 

 and islands of small size, which project, like cones, from the 

 sea-bottom above the surface of the water, and narrow isth- 

 muses, such as Panama and Darien, washed by great oceans, 

 must present a distribution of heat in their rocky strata dif- 

 ferent from that of parts of equal circumference and mass in 

 the interior of continents. In a very elevated mountainous 

 island, the submarine part is in contact with a fluid which 

 has an increasing temperature from below upward. But as 

 the strata pass into the atmosphere unmoistened by the sea, 

 they come in contact, under the influence of insolation and 

 free radiation of dark heat, with a gaseous fluid in which 

 the temperature diminishes with the elevation. Similar 

 thermic conditions of opposed decrease and increase of tem- 

 perature in a vertical direction are repeated between two 



