THE 



AMERICAN JOURNAL OF SCIENCE 



[FIFTH SERIES.] 



Aet. I. — The Relation of Isostasy to Uplift and Sub- 

 sidence;^ by William Bowie, Chief, Division of 

 Geodesy, U. S. Coast and Geodetic Survey. 



Introduction. 



There are many phases of the subject of isostasy, any 

 one of which would make the subject of a paper of an hour. 

 In going over the question as to what I should talk about 

 to-night, I reached the conclusion that it would be better 

 not to tire you with details of the observations and compu- 

 tations involved in the isostatic investigations but to 

 show, in a general way, what are the data, what is their 

 reliability and what are the logical conclusions which 

 may be drawn from the results of the investigations. 



The figure of the earth. 



We should first consider the shape and size of the earth 

 before we can understand how geodetic observations 

 furnish data for the study of the distribution of densities 

 in what Bailey Willis has very aptly called the 'isostatic 

 shell.'' 



If the earth were not rotating and its materials were 

 homogeneous mth respect to depth, the actual surface of 

 the earth would be a. true sphere. The earth is rotating 

 and, therefore, the combination of the gravitational force 

 and the centrifugal force would make this ideal earth 

 have a surface which would be a spheroid of revolution. 



As a matter of fact, the densities, at least in the outer 



^ Paper read before the Geological Club of Yale IJniversity, February 10. 

 192L ^ ' 



Am. Jour. Sci.— Fifth Series, Vol. II, No. 7.— July, 1921 

 1 



