VOLUME XXVIll 



THE 



NUMBERS 



Journal of Geology 



A Semi-Quarterly 



Edited By 

 thomas c. chamberlin and rollin d. salisbury 



With the Active Collaboration of 



STUART WELLER, Invertebrate Paleontology ALBERT JOHANNSEN, Petrology 



ROLLIN T. CHAMBERLIN, Dynamic Geology 



ASSOCIATE EDITORS 



SIR ARCHIBALD GEIKIE, Great Britain 



CHARLES BARROIS, France 



ALBRECHT PENCK, Germany 



HANS REUSCH, Norway 



GERARD DeGEER, Sweden 



T. W. EDGEWORTH DAVID, Australia 



BAILEY WILLIS, Leland Stanford Junior University 



CHARLES D. WALCOTT, Smithsonian Institution 



JOSEPH P. IDDINGS, Washington, D.C. 



JOHN C. BRANNER, Leland Stanford Junior University 

 RICHARD A. F. PENROSE, Jr., Philadelphia, Pa. 

 WILLIAM H. HOBBS, University of Michigan 

 FRANK D. ADAMS, McGill University 

 CHARLES K. LEITH, University of Wisconsin 

 WALLACE W. ATWPOD, Harvard University 

 WILLIAM H. EMMONS, University of Minnesota 

 ARTHUR L. DAY, Carnegie Institution 



FEBRUARY-MARCH 1920 



THE ORIGIN OF GUMBOTIL 



George F. K.a.y .^xd J. Newton Pearce 



J1IASTR0PHISM AND THE FORMATIVE PROCESSES. XI. SELECTIVE SEGREGA- 

 TION OF TklATERIAL IN THE FORMATION OF THE EARTH AND ITS NEIGH- 

 BORS ------ T. C. Ch.amberlin 126 



A QUANTITATIVE MINERALOGICAL CLASSIFICATION OF IGNEOUS 



ROCKS— REVISED. PART II - - - - - - ■ - Albert Joh.axxsen 158 



REVIEWS - - - - 178 



RECENT PUBLICATIONS ' 182 



THE 



UNIVERSITY OF CHICAGO 



CHICAGO, ILLINOIS, U.S.A. 



PRESS 



THE CAMBRIDGE UNIVERSITY PRESS, London 



THE MARUZEN-KABUSHIKI-KAISHA, Tokyo, Osaka, Kyoto, Fukcoka Sendai 



THE MISSION BOOK COMPANY, Shanghai 



