THE FUTURE OF THE DRY LAND. 247 



pares away the continental masses. Mr. J. Murray, of Scotland, 

 from the study of all that has been published on this subject, of 

 which he has himself furnished a considerable proportion, has 

 found that the outflow of the nineteen principal rivers of the 

 earth is 3,610 cubic kilometres a year. These 3,610 cubic kilo- 

 metres bring to the sea a mass of solid matter in suspension 

 equivalent to one cubic kilometre and i^o* making a proportion 

 in value of 38 parts per 100,000. On the other hand, meteorologi- 

 cal observations have become precise enough to enable us to esti- 

 mate approximately the annual outflow of all the rivers of the 

 earth. Mr. Murray puts it at 23,000 cubic kilometres. Applying 

 to this figure the same proportion of 38 per 100,000, we get, for the 

 amount of solid matter annually carried mechanically to the sea 

 by rivers, 1,043 cubic kilometres. That is the effect of the me- 

 chanical action of the continental waters. 



What part do the waves of the ocean take in this action ? 

 When we hear the noise of the waves breaking against the bluffs 

 and throwing their grape-shot of pebbles against them, and when 

 we witness the enormous land-slides of which the sea-shores are 

 often the theatre, we are sometimes led to think that the action 

 of the sea is a preponderant factor in the destruction of conti- 

 nents. But the reverse is the case. 



England may be regarded as one of the countries in which 

 attacks by the sea upon the coast are most intense ; for the waves 

 of the Atlantic are thrown very violently against the shore by 

 the southwest winds. English geologists appear to be agreed in 

 thinking that the waste of the coasts of Britain under the action 

 of the sea is certainly not more than three metres a century. It 

 is true that at certain points of the French littoral, as at Havre, 

 the banks are estimated to lose a quarter of a metre a year. M. 

 Bouquet de la Grye raises the loss to a little more than a metre a 

 year on the limestone coasts of the southwest ; but, in compensa- 

 tion, there are seas where the work of the waves may be neglected 

 as null, as well as flat coasts, where the sea, building up littoral 

 bars, adds instead of taking away. I believe, then, till the con- 

 trary is proved, that if we allow for the whole earth a waste of 

 three metres in a hundred years, we are above rather than below 

 the truth. 



If we suppose that the shore-banks average fifty metres in 

 height, it follows that an annual waste of three centimetres will 

 remove a cubic metre and a half per running metre, or 1,500 cubic 

 metres per kilometre. The extent of the sea-coasts of the earth 

 can be easily calculated with the aid of the figures given in Elise'e 

 Reclus's Continents, showing the proportion, in each continental 

 unit, of dry-land surface and extent of coast-line. Applying 

 these figures to those which represent the surface, now well 



