246 THE POPULAR SCIENCE MONTHLY. 



THE FUTURE OF THE DRY LAND.* 



Br M. A. de L' APPARENT. 



I PURPOSE to inquire briefly into the probable future of the 

 dry land, to ask if it is not destined to disappear, and to esti- 

 mate the time that may be required to execute a sentence of ex- 

 tinction against it. It would have been hazardous to touch upon 

 this question a few years ago. Precise data were wanting as to 

 both the value of the relief of the land and the intensity of the 

 actions which are called into play to change it. But the progress 

 of geographical study has now put us in possession of more ex- 

 act information, enough to permit us to seek a solution of the 

 problem, not in the expectation of getting exact figures, but of 

 calculating approximately the magnitude of the effects which we 

 have to contemplate. 



The labors of geographers in later years have given us a much 

 more complete knowledge than we had before of the land relief. 

 Ten years ago we still accepted Humboldt's estimate that, if all 

 the asperities of the land were leveled over its entire surface, the 

 resultant plateau would stand 305 metres above the surface of the 

 sea. This figure began to grow perceptibly about 1880. A Ger- 

 man student, Herr Krummel, raised it to 444 metres. A few years 

 ago, I thought it best, in preparing the chapter in my Traite* de 

 Geologie bearing upon this subject, to go into new calculations on 

 the basis of existing hypsometric maps, and I came to the con- 

 clusion that the mean altitude of the dry land would be more than 

 500 metres, and would probably approach 600 metres. I declared 

 this result with some reserve, on account of its novelty. But I 

 had the satisfaction of seeing it immediately accepted by foreign 

 geographers, and my estimates have since been exceeded; for 

 Messrs. John Murray, Penck, Supan, and De Tillo, having been 

 able, by the aid of the cartographic documents accessible to them, 

 to make still more precise calculations, have found that the land 

 relief may be represented by a uniform plateau rising to 700 

 metres above the level of the sea. 



This plateau of 700 metres is the object of incessant attacks by 

 the ocean on one side and atmospheric agents on the other. The 

 rivers never cease carrying to the sea the fine fragments of the rocks 

 which the rain washes into them, after they have been disinte- 

 grated by the alternate actions of moisture and drought, cold and 

 heat, freezing and thawing. By observation of what takes place 

 at the mouths of rivers, we may succeed in reaching a clear idea 

 of the measure in which the silent action of atmospheric agents 



* Address before the Geographical Society of Paris. 



