VOLUME XXIV 



THE 



NUMBER i 



Journal of Geology^ 



A Semi-Quarterly 



Edited By 

 thomas g. chamberlin and rollin d. salisbury 



With the Active Collaboration of 



SAMUEL W. WILLISTON 



Vertebrate Paleontology 



STUART WELLER 



Invertebrate Paleontology 



ALBERT JOHANNSEN 



Petrology 



ROLLIN T. CHAMBERLIN 



Dy^Cec^^ ""* 



ASSOCIATE EDITORS 



COLLEC >• 



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 



GROVE K. GILBERT, Washington, D.C. 



CHARLES D. WALCOTT, Smithsonian Institution 



HENRY S. WILLIAMS, Cornell University 



JOSEPH P. IDDINGS, Washington, D.C. 

 JOHN C. BRANNER, Leland Stanford Junior University 

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

 WILLIAM B. CLARK, Johns Hopkins University 

 WILLIAM H. HOBBS, University of Michigan 

 FRANK D. ADAMS, McGill University 

 CHARLES K. LEITH, University of Wisconsin 

 WALLACE W. ATWOOD, Harvard University 

 WILLIAM H. EMMONS, University of Minnesota 

 ARTHUR L. DAY, Carnegie Institution 



JANUARY-FEBRUARY 1916 



THE ACADIAN TRIASSIC. PART I - Sidney Powers i 



AVERAGE REGIONAL SLOPE, A CRITERION FOR THE SUBDIVISION OF OLD 

 EROSION SURFACES ---------- Leopold Reinecke 27 



CAIMANOIDEA VISHERI, A NEW CROCODILIAN FROM THE OLIGOCENE OF 

 SOUTH DAKOTA - - - Maurice G. Mehl 47 



ON THE STRUCTURE AND CLASSIFICATION OF THE STROMATOPOROIDEA 



M. Heinrich 57 



THE PHYSIOGRAPHY OF MEXICO - - - - - - Warren N. Thayer 61 



REVIEWS ---------- 95 



THE UNIVERSITY OF CHICAGO PRESS 



CHICAGO, ILLINOIS, U.S.A. 



Agents 



THE CAMBRIDGE UNIVERSITY PRESS, London and Edinburgh 



KARL W. HIERSEMANN, Leipzig 



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



