406 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1910. 



If we apply these considerations to the question with which this 

 review began, What are the foundations of the earth? We may 

 answer: The foundations are solid rock, which is self-crushed to a 

 depth of 120 kilometers, more or less, which is rendered sufficiently 

 rigid by pressure to maintain its form during prolonged geologic 

 periods with but very slight change, in spite of stresses occasioned 

 by erosion of continental reliefs, but which is capable of movements 

 that from time to time result in the gi'adual elevation of continents 

 and the more vigorous uplifts of mountains through which isostatic 

 equilibrium is restored. 



