90 PROCEEDINGS OF THE CHICAGO MEETING 



takeu in conjunction witli laboratory determinations of the resistance to abra- 

 sion of these and other pebbles and measurements of the shapes of those peb- 

 bles, permits an estimate to be made of the distance traveled by the latter. 

 Similarly, estimates have been made with reference to the persistence of 

 glacial strife during subsequent stream transportation of the pebbles, and other 

 applications of this study have been made. In these estimates many assump- 

 tions are made concerning unknown factors which await evaluation from 

 future studies of this sort, but the results, even with these limitations, are 

 significant. 



Presented without notes, with lantern-slide illustration. 

 Discussed by Dr. J. A. Udden. 



REGIONAL STRUCTURE IN NORTH-CENTRAL TEXAS 

 BY E. H. SELLARDS 



(Adstract) 



The paper relates to regional structure in north-central Texas as determined 

 from well records. The underground position of the pre-Cambrian formations 

 is determined over a limited area adjacent to the Llano uplift in central Texas 

 and in three counties adjacent to the Red River in northern Texas. The 

 underground position of the Cambro-Ordovician formations is determined over 

 a considerable area in north-central Texas. The regional structure is illus- 

 trated by one north-south and three east-west sections. 



Presented in abstract without notes. 



PALEOGEOGRAPHY AND CORRELATION OF THE MARINE TERTIARY DEPOSITS 



OF THE WEST COAST 



BY BRUCE L. CLARK 



{Abstract) 



The purpose of this paper is to give a summary of the data up to date per- 

 taining to the paleogeography and correlation of the marine west coast Ter- 

 tiary deposits. Eleven paleogeographic maps will be presented with the paper, 

 together with a tentative correlation table. 



The aggregate thickness of the west coast Tertiary deposits exceeds 40,000 

 feet. The sediments, which for the most part consist of clastic materials, were 

 laid down in geosynclinal troughs, a condition very similar to that which ex- 

 isted along the east coast of North America during the Paleozoic. Crustal 

 movements were going on more or less interruptedly throughout the entire 

 Tertiary period. The sea invaded and retreated many times from these inland 

 basins. The contact between the deposits of these different cycles of deposi- 

 tion are usually well marked — in fact, in a large percentage of cases they are 

 indicated by angular unconformities. 



Presented in abstract without notes, with lantern-slide illustration. 



