THE WASTE AND GAIN OF THE DRY LAND. 407 



will wholly disappear in four or five million years. Geology 

 teaches us that the history of the crust of the earth embraces a 

 period infinitely longer than this. That is enough to prove that 

 another factor does intervene that is, manifestations of internal 

 energy, which disturb from time to time the acquired states of 

 equilibrium, and restore a new force to the decreasing outer pow- 

 ers. Thus, instead of assuming a regular process of planing down, 

 I laid down in principle that things would not go on in this way. 

 A geologist, besides, could not reason otherwise, except he mis- 

 took the daily teachings of science which show him at every in- 

 stant foldings and contortions of strata, certain signs of an order 

 of things very different from the regular pursuit of external in- 

 fluences. 



" Seeking, then, to place myself under the most unfavorable con- 

 ditions for my theory, I supposed the ancient history of the globe 

 divided into tranquil periods, each of four or five million years, 

 separated from one another by so many ruptures of equilibrium. 

 How many of these periods would be required to account for all 

 the known sedimentary formations ? In trying to solve this prob- 

 lem, I remarked that each period would have cast into the ocean 

 a cube of debris which, scattered, according to Mr. J. Murray, 

 through only one fifth of its area (the fraction over which, ac- 

 cording to the soundings, the sedimentation of detritus extends), 

 would form a bed of some six or seven hundred metres in mean 

 thickness. It seemed to me reasonable to suppose that this thick- 

 ness, null at the extreme further side of the deposits, would in- 

 crease slowly at first, and then more rapidly toward the neighbor- 

 hood of the coast, where it might attain a maximum of two kilo- 

 metres. Dana having estimated at forty-five thousand metres the 

 united depth of all the sedimentary formations when each is meas- 

 ured at its point of greatest thickness, I drew the conclusion that 

 all geological history could be included within a time certainly 

 less than ninety million years. After the publication of this note 

 I was called upon by the general secretary of the Geographical So- 

 ciety to supply the place of a speaker who was unable to fulfill his 

 engagement. I responded, undertaking to call the attention to the 

 phenomena of erosion which I had been studying, without elabo- 

 rating the purely geological considerations. I have recently pre- 

 sented an extended paper on these details to the Catholic Interna- 

 tional Scientific Congress, and in it have examined all the phases 

 of the question. This paper will be published in full, and in it 

 M. Ldotard will be able to learn how greatly my views differ from 

 those which he has mistakenly attributed to me. 



" I will here only correct a grave error which my critic commits 

 when he charges me with not having taken account of the accre- 

 ment which volcanic action brings to the dry land. M. Le'otard 



