Reviews 



The Earth a Failing Structure. Presidential Address before the 

 Philosophical Society of Washington. By John F. Hayford. 

 Bulletin of the Philosophical Society of Washington, D. C, 

 Vol. XV, pp. 57-74, December, 1907. 



The title of the address clearly expresses its central thought. The 

 endeavor is to show that the earth is not a competent elastic structure. 

 The main basis of argument is that, in the past, the earth has yielded 

 frequently, if not continuously, to the stress-differences brought to bear 

 upon it, and that it is still yielding. This yielding is repeatedly spoken of 

 as non-elastic, but specific evidence is not given that the yielding is strictly 

 of the non-elastic type. Every geologist will accept the fact of yielding 

 without hesitation, but some of us might be disposed to question the pre- 

 cise method by which the yielding takes place, for it is just at this point 

 that discrimination now halts for adequate evidence, and it is just here 

 that some of the greatest advances in deformation appear now to be on 

 the verge of realization. If the conclusion that the earth is a failing struc- 

 ture can be safely based on the gross observation that it, or parts of it, 

 have yielded to stresses in the past, there can be little ground for difference 

 of view, and little occasion to regard the view as new except in its form 

 of expression, and we may all acquiesce in the striking text of the address. 



At the same time it may be said with equal deference to observed fact 

 that the earth is a creative structure and that it long has been and still 

 is generating structural strength, elasticity, and rigidity. On the whole, 

 its creative activities seem to have been quite as pronounced as its failing 

 tendencies; its acquisitions of competency to have been quite as great 

 as its exhibitions of incompetency. 



Perhaps nothing better represents a failing structure, in the sense of 

 the address, than a glacier which, under normal conditions, is ever yielding 

 to the stress of gravity. And yet if one wanted to select a cubic foot of 

 ice which had the maximum of strength and rigidity and the highest elastic 

 limit, he would seek it at the lower end rather than the upper end of the 

 glacier. The structural competency of the ice normally increases in about 

 the proportion in which it has previously failed as a competent elastic 

 structure, if one so interprets its yielding. 



If a sandstone be sufficiently stressed, it will perhaps seem to fail as 

 a structure, but the quartzite into which it might pass would doubtless 



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