THE 



JOURNAL OF GEOLOGY 



A Semi-Quarterly Magazine of Geology and 

 Related Sciences 



Editors 



T. C. CHAMBERLIN, in General Charge 

 R. D. SALISBURY R. A. F. PENROSE, Jr. 



Geographic Geology Econotnic Geology 



ALBERT JOHANNSEN C. R. VAN HISE 



Petrology Structural Geology 



STUART WELLER W. H. HOLMES 



Paleontologic Geology Atzthropic Geology 



S. W. WILLISTON, Vertebrate Paleontology 



Associate Editors 

 sir archibald geikie g. k. gilbert 



Great Britain ■ Washington, D. C. 



H. ROSENBUSCH H. S. WILLIAMS 



Germany Cornell University 



CHARLES BARROIS C. D. WALCOTT 



France U. S. Geological Survey 



ALBRECHT PENCK J. C. BRANNER 



Germatty Stanford University 



HANS REUSCH W. B. CLARK 



Norway Johns Hopkins University 



GERARD DE GEER O. A. DERBY 

 Sweden Brazil 



T. W. E. DAVID 

 Australia 



VOLUME XVIII 



CHICAGO, ILLINOIS 



