INTERNATIONAL GEOLOGIC INSTITUTE 603 



the local attitude of the land to the sea without affecting the 

 capacity of the ocean basin, for the warping up in one region 

 may be compensated by the warping down in another region. 

 The subject is therefore attended by grave difficulties, but it is 

 not without sufficient ground of hope to justify systematic study. 

 There are at least two general phases of earth-action whose 

 effects promise to rise above those of local warpings to such a 

 decree as to be determinable and to be serviceable in interconti- 

 nental correlation. They 2re the stages of great shrinkage and 

 the stages of relative quiescence. Whatever views may be enter- 

 tained of the early history of the earth or of its internal con- 

 stitution, it will probably not be questioned that the oceanic 

 bottoms have, on the whole, shrunk more than the continental 

 platforms. The very existence of the continents in spite of 

 erosion is an expression of this. It will perhaps not be denied 

 that the shrinkage adjustments of the exterior of the earth have 

 been periodic and that the basins have been deepened and the 

 land relatively elevated at the periods of adjustment ; at any 

 rate, this may be made a working hypothesis, coordinately with 

 its opposite, until the truth is ascertained. 



Between the assumed periods of adjustment, periods of rela- 

 tive quiescence may be recognized as their necessary comple- 

 ment. These were only relatively quiescent, for local and 

 regional warpings were quite certainly in progress at all stages 

 of geological history. In these stages of relative quiescence the 

 volumetric erosion of the land may quite safely be assumed to 

 have exceeded the volumetric elevation, and the material trans- 

 ported to the sea may be assumed to have exceeded any increase 

 of the capacity of the ocean basin due to shrinkage. Without 

 these assumptions it seems to me difficult to explain specifically 

 the history of erosion and sedimentation ; but, as this may be 

 doubted, let the assumptions stand merely as working hypoth- 

 eses. The result of such erosion would be the partial filling of 

 >the common ocean basin and the extension of the sea upon the 

 land. Taking Murray's estimate of the present average height 

 of the land, a volumetric reduction and transference of one half 



