CONTENTS 



Page 

 Origin and composition of certain oil sliales [abstract and discus- 

 sion] ; by Reinhardt Tliiessen 72 



Session of Thursday afternoon, December 30 74 



Discussion of Doctor Tliiessen's paper continued 7i 



Titles and abstracts of papers presented at tlie afternoon session and 



discussions thereon 74 



Demonstration material in geology [abstract] ; by H. P. Cleland. 74 

 Cryptovolcanic structure in Ohio of the type of the Steinheim 



Basin [abstract] ; by Walter H. Bucher 74 



Probable cause of the localization of the major geosynclines [ab- 

 stract] ; by Walter H. Bucher 75 



Postglacial faulting about Mount Toby, Massachusetts [entire, 



with discussion] ; by F. B. Loomis 75 



Significance of the relation of proboscidean remains to the sur- 

 face of Nebraskan gumbotil, near Osceola, Clarke County, Iowa 



[entire, with discussion] ; by George F. Kay S0_ 



Vote of thanks S?> 



Preliminary sketch of the history of the lower Missouri [entire] ; 



by Frank C. Greene l 83 



Post-Illinoisan drift in northern Illinois west of the mapped Wis- 

 consin moraine [abstract] ; by Morris Leighton 86 



Origin and history of Lake Chelan [abstract] ; by J. J. Runner.. 87 

 Ancient rock deformations and their present expressions in west- 

 ern Vermont [abstract] ; by Clarence E. Gordon 88 



Method of measuring and plotting the shapes of pebbles [ab- 

 stract] ; by Chester K. Wentworth 89 



Field study of the shapes of river pebbles [abstract] ; by Chester 



K. Wentworth 89 



Regional structure in north-central Texas [abstract] ; 1^ E. H. 



Sellards 90 



Paleogeography and correlation of the marine tertiary deposits of 



the west coast [abstract] ; by Bruce L. Clark 90 



Probability of Pennsylvanian glaciation of the Arbuckle and 



Wichita Mountain regions [abstract]; by Samuel Weidman... 91 

 Devonian black shales of western New York [abstract] ; by 



George H. Chadwick 91 



Register of the Chicago meeting, 1920 92 



Constitution and By-Laws , 94 



Publication rules 101 



Officers, Correspondents, and Fellows of the Geological Society of America 105 



Session op Tuesday, December 28, 1920 



The Thirty-third Annual Meeting of the Geological Society of America 

 was held December 28-30, 1920, in Chicago, Illinois, in affiliation witli 

 the Seventy-third Annual Meeting of the American Association for tlie. 



