September-October 1920 Vol. XXVIIl, No. 6 



The Journal of Geology 



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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