EDITORIAL 667 



unfamiliar with the weaknesses of their armor. In the Strength 

 of the Earth'' s Crust Barrell demonstrated the character and quahty 

 of his mind. He was a great analyst. 



It is of interest to contrast Barrell's method with Gilbert's in 

 the discussion of the fundamental problems of isostasy. Gilbert 

 was a co-worker with Button in the studies that gave birth to the 

 concept. Button formulated the idea of isostasy in 1889, and 

 Gilbert discussed the related problem of crustal strength in 1890 

 in Lake Bonneville, the manuscript of which, so far as it touched 

 this subject, was under consideration in 1888 and earher. Gilbert's 

 last contribution to the subject was in 19 13. It is a brief but 

 comprehensive interpretation of anomahes of gravity. In the 

 interval of twenty-five years he wrote but little on isostasy, al- 

 though he was associated with Putnam in the initial studies of 

 gravity intensities in the United States and followed Hayford's 

 brilliant work with constant interest. He published far less in 

 a quarter of a century of investigation than Barrell has given us in 

 one group of articles. Barrell's analysis covers every part of the 

 subject exhaustively, dissociates all its elements, weighs them, 

 and recombines them. It is the product of extraordinary industry, 

 activity, and thoroughness. Gilbert, a profound thinker, a 

 philosopher, awaited patiently the unfolding of knowledge. He 

 entered into no controversy. Nothing escaped him, but he was 

 content to sketch the edifice of truth in terms of fundamental 

 principles. He anticipated Barrell in conclusions as to the relative 

 importance of rigidity and isostasy, which the latter's exhaustive 

 analysis confirmed. 



A work comparable in exhaustive treatment with Barrell's 

 Strength of the Earth^s Crust is his Rhythms and Geologic Time. 

 Rhythms in denudation and rhythms in sedimentation are dis- 

 cussed through sixty pages, emphasis being laid upon the pulsatory 

 character of uplifts and subsidences. In contrast to previous 

 discussions the view is developed that "the deposition of nearly 

 all sediments occurs just below the local base level, represented 

 by wave-base or river-flood level, and is dependent on upw^ard 

 oscillations of base level or downward oscillations of the bottom." 

 If this be so, it follows that there are numerous interruptions in the 

 process of sedimentation, some of which are already known as 



