248 THE POPULAR SCIENCE MONTHLY. 



known, of the different countries, we get 200,000 kilometres as 

 the total length of the coast-lines. Hence, the supposed loss of 

 1,500 cubic metres per kilometre per year would give 300,000,000 

 cubic metres, or three tenths of a cubic kilometre. Thus, while 

 the running waters take away ten and a half kilometres, the sea 

 does not remove one twentieth of that quantity. Even supposing 

 I have underestimated the height of the coast-banks, and have 

 not given enough importance to the annual waste, let the figures 

 I have used as the base of my calculations be tripled, we still find 

 the effect of sea action a mere fraction, hardly significant, of that 

 which is produced by the silent wash of the rivers. We can say 

 here, as in many other cases, that what does the most work is not 

 that which makes the most noise. 



We have, in addition to this, to consider the solvent action of 

 continental waters. They partially dissolve all the rocks, aided, 

 as they are in the action, by carbonic acid ; and they come to the 

 sea charged with a considerably larger proportion of matter in 

 solution than one would at first be liable to suppose. According 

 to the labors of the English, American, and International com- 

 missions, which have especially studied the composition of the 

 waters of rivers, particularly of the Mississippi, Danube, and 

 Thames, the quantity of solid matters brought down in solution 

 from the continents is not less than five cubic kilometres a year. 

 This, added to the matter carried down mechanically, gives about 

 15 cubic kilometres, or, including the results of marine action, 

 16 cubic kilometres. This, then, is about what the continental 

 masses lose each year. 



Let us consider this supposed uniform plateau standing up 700 

 metres above the level of the sea. By the operation of the circum- 

 stances of which I have spoken, 16 cubic kilometres are taken from 

 this mass every year. The continental surfaces covering 146,000,- 

 000 square kilometres, we calculate that a waste of 16 cubic kilo- 

 metres will remove, each year, a layer -jW f a millimetre thick. 

 The debris from this layer will settle on the bottom of the sea 

 and assume the form of sedimentary deposits ; they will take the 

 place, then, of a corresponding quantity of water, in consequence 

 of which the sea will rise to a certain extent. The ratio of the 

 continental surface being to that of the seas about as 100 to 252, the 

 total result will be a lowering of the height of the plateau of about 

 tWo f a millimetre every year. 



As many times as this $ of a millimetre is contained in 700 

 metres, or 700,000 millimetres, so many years will be required to 

 bring about the disappearance of the dry land. Make the calcula- 

 tion, supposing the present intensity in the phenomena of destruc- 

 tion to continue, and you will find that it will take 4,500,000 

 years to wear the surface of the earth entirely away. This may be 



