THE GEODETIC EVIDENCE OF ISOSTASY 35 



that the earth solidified in comparatively recent time. For other- 

 wise, under the influence of a decreasing rate of rotation, the 

 water would draw away from the equator and leave it high and 

 dry. Now if the earth is so weak that it can stand but a small 

 fraction of the weight of a continent before isostatic readjust- 

 ment begins to take place, of course the equatorial protuberance 

 due to decreasing rotation will be leveled down by failure and 

 isostatic readjustment practically as fast as it develops, even if 

 no other actions tend to level it down. Hence the study of the 

 distribution of land with respect to latitude furnishes a measure 

 of the earth's weakness, not of its age. 



Another speaker quoted an article by Mr. G.Johnstone Stoney 

 in which it is suggested that the permanence of the continents 

 is due to elastic expansion of all the underlying material when 

 load is removed by erosion. This idea, viewed in the light of 

 geodetic evidence, seems to be extremely absurd, for it assumes 

 the earth to be perfectly elastic — a competent structure — to great 

 depths, whereas the earth is apparently inelastic to a high degree 

 even near the surface and is apparently failing continuously 

 under the stresses brought to bear upon it. 



The expression "failing continuously" has been used pur- 

 posely. It is possible that the continents and oceans are in then- 

 present positions because light material accumulated at the out- 

 set in the places now occupied by the continents, and heavier 

 material accumulated where the deep oceans now lie. This 

 would constitute an initial isostatic adjustment. But the geologic 

 evidence is overwhelming that within the interval covered by 

 the geologic record many thousands of feet of thickness have 

 been eroded from some parts of the earth and have been trans- 

 ported to and deposited upon other parts. If isostatic readjust- 

 ment had not also been in progress during this interval, it would 

 be impossible for the isostatic compensation to be so nearly 

 complete as it is at present. 



For example, it is estimated by competent authority that a 

 series of strata from 8 to 10 miles thick have been eroded and 

 carried away from certain areas in the western part of the 

 United States, which are now broad and lofty platforms carry- 

 ing mountain ridges. The present elevation of these areas is 



