222 



JOSEPH BARRELL 



Hayford and Bowie in their successive publications give the follow- 

 ing for the pre-Cambrian and Cenozoic stations, the two groups 



TABLE XIII 



to which the attention will be confined. A few stations of high 

 anomaly must have considerable influence on the result, as most 

 of the stations are used in common in all of the estimates. 



TABLE XIV 



* Fifteen stations have plus anomalies, 17 have minus anomalies. 



Bowie's figures in the American Journal of Science will be used in 

 the following discussion. 



Bowie favors the explanation that these relations of anomahes 

 to geologic formations are due to slight changes of density extend- 

 ing more or less through the zone of compensation and leading to 

 departures from perfect isostasy. The writer, however, is led to 

 favor the view that about one-half of the contrasted anomaly for 

 these two groups is due to a lesser density within the outer mile 

 of crust beneath the Cenozoic stations, as contrasted to the outer 

 mile of crust beneath the pre-Cambrian stations. The remainder 

 of the anomaly it is thought is explained by the ease of erosion of 

 Cenozoic formations, the resistance to erosion of the pre-Cambrian 



