264 On Depressions on the Surface of the Globe. 



soming lakes in their depths, both receiving supplies of river water, but 

 yielding none. The channel of the ocean in the structure and in the di- 

 versity of its surface seems in all respects closely to resemble that of the 

 dry land, which has itself, indeed, at no distant period occupied its depths, 

 and still bears on its surface loads of marine remains. Our lesser islands 

 are but the summits of mountains whose bases rest on the valleys or table- 

 lands far down in the main, presenting at times slopes as smooth and 

 gentle, and precipices and cliffs as lofty, rugged, and abrupt as any of 

 those made visible to the eye of man. The sounding-line discloses hills, 

 mountains and valleys, with chasms and recesses as diversified and re- 

 markable as any which the regions exposed to the upper air supply, 

 covered with a dense and varied vegetation, and thickly peopled with 

 numberless races of stirring inhabitants, to some of which in point of size 

 the giants of the superterrene animal kingdom — the elephant, the giraffe, 

 the rhinoceros, and the hippopotamus — are but pigmies. The mean level 

 of the whole solid land above that of the sea is 1000 feet — that is, were 

 our mountain masses smoothed down, and our valleys and sea margins 

 brought up to one general table-land, its surface would be 1000 feet above 

 that of the ocean. The mean level of Asia is 1150 feet, of that of Africa 

 we know nothing, that of Europe 670, and that of America 930 feet, 

 North America being 750, and South America, 1130. The mean 

 depth of the ocean, again — that is, of its basin, were this scooped out, 

 and smoothed in the floor till it resembled a tank or cistern, is about 

 22,000 feet or four miles. It has been measured to the depth of nearly 

 seven miles, or about 36,000 feet, and it covers three-fourths of the sur- 

 face of the globe. Were the solid part of the earth, therefore, to be 

 removed, and thrown into the sea, the highest mountains would fall 

 short by 10,000 feet of filling up its deepest recesses, and the whole mass 

 would be submerged to the depth of a mile at least. 



Vast as these inequalities are when represented in figures, the relation 

 they bear to the diameter of the earth is insignificant. On that magnifi- 

 cent three- feet globe now before you, on which the hand might cover the 

 whole space anj'thing like tolerably known to us, the highest of theHima- 

 layas would be represented by a grain of sand, and the enormous-look- 

 ing depressions just described, by a scratch which would little more than 

 penetrate the varnish — so very small a way beneath the surface does our 

 knowledge extend, and our research penetrate. Yet this thin film in space 

 furnishes the habitation of all the vegetable and animal tribes that have 

 been formed, and the examination of the minutest portions of it taxes 

 to the uttermost the intellect, and occupies and exhausts the energies of 

 man. 



