Joseph Barrell. 273 



this Journal, J. F. Hayford's paper, "The Geodetic 

 Evidence of Isostasy," and gives a brief historical re- 

 view of the place of this subject in geological literature 

 and of the problems upon which it bears. 



In 1914, Barrell was led to study the theories leading 

 to the conclusion that the poles of the earth are not 

 fixed. Astronomers and some geologists are opposed to 

 the theory of polar wanderings, but students of ancient 

 climates and of the geographical distribution of floras 

 and faunas have been adherents to this view. In his 

 "Status of Hypotheses of Polar Wanderings,' ' Barrell 

 states: "From these considerations it is seen that 

 closer examination tends to cut down more and more 

 even those moderate limits of polar migration set by 

 [the mathematician] Darwin. It would appear that the 

 assumption of polar wandering as a cause of climatic 

 change and organic migrations is as gratuitous as an 

 assumption of a changing earth orbit in defiance of the 

 laws of celestial mechanics." 



During the years 1914 and 1915, Barrell published in 

 the Journal of Geology a series of eight papers that 

 were later collected and bound in one volume under the 

 title "The Strength of the Earth's Crust." This work 

 at once placed him high among the geodesists. Arthur 

 Holmes writes of it as a "remarkable series of papers, 

 which is worthy of the most careful study," and "con- 

 stitutes a valuable and stimulating contribution to 

 terrestrial dynamics." L. V. Pirsson says: "They 

 constitute probably the most serious and profound dis- 

 cussion, which has yet been attempted, of the facts 

 which are known and of the theories which have been 

 deduced from them, concerning the strength of the 

 earth's outer shell." 



The first part of this series of articles treats of the 

 geologic tests of the limits of strength. In Parts II 

 and III is discussed the "Regional Distribution and 

 Influence of Variable Rate of Isostatic Compensation." 

 Part IV deals with the "Heterogeneity and Rigidity of 

 the Crust as Measured by Departures from Isostasy," 

 while Part V is on the "Depth of Masses producing 

 Gravity Anomalies and Deflection Residuals." Part VI 

 is devoted to the "Relations of Isostatic Movements to 

 a Sphere of "Weakness — the Asthenosphere," and Part 

 VII to "Variation of Strength with Depth, as Shown 



