194 COSMOS. 



As regards the area which they occupy, however, mountains 

 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 re- 

 gions 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 coldness. Exact ob- 

 servations 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 80.6, water of the temperature of 36.5 could 

 be drawn up from a depth of seven or eight hundred fathoms, 

 phenomena which prove the existence of under currents 

 from the polar regions. The consequences of tliis constant, 

 suboceanic refrigeration of by far the greater part of the 

 crust of the earth deserve a degree of attention which they 

 have not hitherto received. JRocks and islands of small size, 

 which project, like cones, from the sea-bottom above the sur- 

 face of the water, and narrow isthmuses, such as Panama and 

 Darien washed by great oceans, must present a distribution 

 of heat in their rocky strata, different from that of parts of 

 equal circumference and mass in the interior of continents. 

 In a veiy elevated mountainous island, the submarine part is 

 in contact with a fluid which has an increasing temperature 

 from below upwards. But as the strata pass into the atmo- 

 sphere, 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 temperature in a vertical direction 

 are repeated between two large inland seas, the Caspian and 

 Aral Sea, in the narrow Ust-tJrt, which separates them from, 

 each other. In order, however, to clear up such compli- 

 cated phenomena, the only means to be employed are such 

 as borings of great depth, which lead directly to the know- 

 ledge of the internal heat of the earth, and not merely ob- 

 servations of springs, or of the temperature of the air in 

 caves, which give just as uncertain results as the air in the 

 galleries arid chambers of mines. 



