252 CHAMBERLIN— THE AGE OF THE EARTH. 



comparing the faunas below them with those above, but this falls 

 within the province of my paleontological colleague, and I therefore 

 leave this source of correction in his hands, merely expressing the 

 conviction that these breaks in the continuity of the sediments are 

 quite sure, when finally and fully adjudicated, to extend greatly the 

 old estimates of the time occupied in sedimentation. 



2. Human Acceleration of the Rate of Deposition. — To pioneers 

 who watched the effects of floods, freshets and ordinary wash on the 

 native surface of our prairies and forests in their virgin state, and 

 who are able now to compare this with the present wash of the same 

 surfaces under cultivation, there is no need to argue that human 

 intervention has greatly hastened denudation and deposition. In the 

 native state the surface was protected by thick mats of grass, leaves 

 and other vegetal debris ; while the soil was bound together by dense 

 entanglements of roots. The waters then ran almost clear where now 

 they run mud.^ Added to this are the quickened deflation of winds, 

 the wear of roadways, the effects of quarrying and other excavation, 

 as well as the actual carting away of clays, sands, gravels, quarry 

 stone, foodstuffs, timber, and other material. While it is not easy 

 to fix on a definite measure of these effects, the needed correction 

 seems certainly to be large. 



3. Correction for the Present Elevation of the Surface. — It is 

 held by leading American geologists that the general elevatory move- 

 ments of the continents have alternated with periods of relative 

 stability during which the processes of base-leveling and sea-trans- 

 gression have cut down the continents and developed peneplains.^" 



9 A fuller statement of this with citations of data from Dole and Stabler 

 and from F. W. Clarke is given in " Diatrophism and the Formative Proc- 

 esses, Vni., The Quantitative Element in Continental Growth," T. C. Cham- 

 berlin, Jour. Geo!., Vol. XXII. (1913), PP- 522-28. 



10 The following group of papers emphasize the rhythmical nature of ele- 

 vation and stability and of the action of the atmosphere and hydrosphere 

 upon the periodic deformations of the earth body and thus form the basis for 

 the arguments in this and the next section : " A Group of Hypotheses Bearing 

 on Climatic Changes," T. C. Chamberlin, Jour. Geo!., Vol. V. (1897), pp. 681- 

 83; "The Ultimate Basis for Time Divisions and the Classification of Geo- 

 logic History," ibid., Vol. VI. (1898), pp. 449-^3; "A Systematic Source of 

 Provincial Faunas," ibid., Vol'. VI. (1898), pp. 597-609; "The Influence of 

 Great Epochs of Limestone Formation upon the Constitution of the Atmos- 



