THE GEODETIC EVIDENCE OF ISOSTASY 39 



compressive stresses exerted in a horizantal direction in surface 

 strata, on the other side. The shortening of the surface strata 

 by bending is a record of the extent to which the surface strata 

 have suffered in the contest. 



According to this theory the undertow should be most power- 

 ful a short distance inside the continental borders and hence the 

 mountain building should be most active there. Many geolo- 

 gists have stated this to be the fact. 



Again, according to this theory, such mountain ranges should 

 be unsymmetrical, thereby indicating that the pressure came 

 from the ocean side. Again, according to the geologists, many 

 mountain systems show this effect as, for example, the Alle- 

 ghenies. 



Many other points might be brought out. But the time is 

 too short. 



So, too, the time has been too short to credit ideas to their 

 originators, some of whom are present here to-night. I have 

 tried simply to marshall the ideas and facts in such a way that 

 their relations would become evident. 



Discussion. 

 By Major Clarence E. Dutton. 



I have only words of praise for the paper of Mr. Hayford. He 

 seems to have expressed very accurately the conception of isostasy. 

 His definitions of isostatic adjustment and isostatic compensation are 

 very good. The chief point in his paper which makes it a valuable 

 contribution to science is his determination of the depth at which the 

 compensation occurs and is probably limited. That determination 

 proves to be of a greater depth than f had anticipated, but it is none 

 the less satisfactory on that account. Indeed I think it is more satis- 

 factory than I had anticipated. It gives a greater concentration to the 

 isostatic effort and permits us to infer a larger amount of horizontal 

 displacement in the underlying masses than if it were much deeper. 

 Also his determination of the amount of strain to which the rocks are 

 subject is very much less and the amount of outstanding deformation 

 of the earth is correspondingly less than we could have reasonably 

 expected. 



I have never supposed that isostasy was a force or condition which 

 produced great elevations and subsidences of the earth. I^have always 



