4 o 4 THE POPULAR SCIENCE MONTHLY. 



the compensating forces, he recognizes their existence and their 

 title to be considered. If we understand him aright, his article 

 was designed to be tentative, and as opening the way to a discus- 

 sion in which much may be said on both sides. 



The discussion which follows will help to give more light con- 

 cerning M. de L'Apparent's views and meaning and their value. 



M. Jacques Ldotard has written in the Revue Scientifique that 

 M. de L' Apparent has in his evidently very curious study arrived 

 at his result only by neglecting several factors of contrary effect. 



While it is admitted that the earth is swept by powerful at- 

 mospheric agents which, if their work was continued without 

 compensatory action on the other side, would ultimately level and 

 submerge all the continents, M. Ldotard insists that there exist 

 other very important causes of increase of the relief, the action 

 of which now counterbalances and may ultimately surpass that 

 of the solvent influences. 



One of these causes, of which M. de L' Apparent took some no- 

 tice, is the contribution of volcanic products to the soil It is one 

 of the most minute of the factors, but M. de L'Apparent's estimate 

 of one sixth of a cubic kilometre a year seems too small. The 

 three hundred known active volcanoes on the surface of the earth 

 ought to give out a much larger quantity of their internal prod- 

 ucts ; and it should be remarked that the dejections of craters, 

 besides lavas, comprise various rocks, mud, and ashes. But the 

 importance of this factor, little at the most, is made still less by 

 the occurrence of volcanic explosions on the sea-coast, in which 

 considerable tracts of land have been swallowed up. 



The chief essential cause of increase of dry land at the ex- 

 pense of the ocean lies in the evolution of our planet. During 

 the geological epochs of thousands of centuries each the up- 

 heavals which formed existing continents have come in gradual 

 succession, taking from the primitive sea, which originally ex- 

 tended over the whole earth, a larger and larger part of its im- 

 mense domain. These upheavals, under the action of internal 

 forces, have continued slowly till our own time in many regions, 

 notably in the north and center of the Scandinavian Peninsula, 

 Spitsbergen, northern Siberia, Turkistan, Scotland, Sardinia, Tu- 

 nis, on the coasts of the Red Sea, etc., while the depressions of 

 vast countries, which must not be confounded with little local 

 collapses produced by the subterranean work of water, are less 

 numerous. Besides the increase of continents, new islands of 

 volcanic origin rise at times to the surface of the seas, and lands 

 are also gradually formed by the accumulation of sedimentary 

 matter and organic remains. The deltas which rise at the mouths 

 of large rivers in consequence of the deposition of mud and sand 

 transported by the streams, likewise constitute an augmentation 



