May-June 1920 Vol. XX VIII, No. 4 ' 



The Journal of Geolog ' 



Edited By 

 thomas c. chamberlin and rollin d. salisbury 



With the Active Collaboration of 



STUART WELLER ALBERT JOHANNSEN 



Invertebrate Paleontology , Petrology 



ROLLIN T. CHAMBERLIN 



Dynamic Geology 



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