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less unsatisfactory, because it involves some assumptions which are 

 apparently incompatible with the necessary deductions of physics, 

 and which must probably be abandoned, whatever may happen to 

 speculative views of the earth's genesis. For example, it is assumed 

 that there is now an inner nucleus of uniform density forming a per- 

 fect spheroid, and that the outer surface that is now the ocean bottom 

 was originally nearly or quite on a level with that on the continents, 

 and that the present oceanic depressions are the result of progressive 

 sinking due to cooling. Lord Kelvin, however, is authority for the 

 statement that "there seems to be no possibility that our present day 

 continents could have risen to their present heights, or that the surface 

 of the solid in its other parts could have sunk down to their present 

 ocean depths, during the twenty or twenty-five million years which 

 may have passed since the consistentior status began or during any time 

 however long." (On the Age of the Earth as an Abode Fitted for 

 Life, p. 706.) And this conclusion is supported by independent con- 

 siderations. The thickness of the earth's crust is taken by Professor 

 Schietz to be 0.02 of the earth's radius, or about eighty miles. If as 

 supposed it rests upon a spheroidal nucleus of uniform density and per- 

 fect form, the difference in thickness in different parts amounts to 

 fully 10 per cent, of its own thickness when reckoned only between 

 plateaus and antiplateaus, neglecting mountain heights. A difference 

 of contraction to the amount of 10 per cent, is quite incredible, as is 

 also any remote approach to this amount. The average difference 

 between the thickness of the crust beneath the continental plateaus 

 and that beneath the ocean bottoms is, under the assumption made by 

 the author, more than 3 per cent, of the whole crustal thickness, and 

 this is more than can reasonably be attributed to any difference in con- 

 traction due to cooling. In view of these and other considerations, it 

 would have been more satisfactory if the discussion had been extended 

 to the postulates of other hypotheses of the inner constitution of the 

 earth : among them, the assumption that an uneven distribution of 

 density reaches to profound depths. 



Nevertheless, it is a great gain to the study of the earth's dynamics 

 that a treatment of the problem from the point of view of pendulum 

 data extended to the ocean surface has been ventured, even though it 



be confined to a single line of hypothetical postulates. 



T. C. C. 



