66 PROCEEDIXGS OF THE AXX ARBOPx MEETIXG 



CRYSTALLINE ROCKS OF THE PLAIXS 

 BY CHARLES X. GOULD 



Presented in fnll extemporaneously. 



Brief remarks were made by Prof. R. S. Knappen. 



PRECA2IBRIAX FOLDIXG IX XORTH AMERICA 

 BY WLLLIAM J. MILLER 



Presented in fiill extemporaneously. 



Eemarks were made by Messrs. Euedemann (by letter) and Coleman 

 and by Miss Fuller, with reply by the author. 



XOTES OX THE SALT DOMES OF XORTH AMERICA 

 BY E. DE GOLYER 



(Ahstract) 



A paper describing the occurrence and structure of the salt domes of the 

 Gulf coastal region of the United States and the Tehuantepec region of Mex- 

 ico, with a discussion of theories of salt dome origin and a comparison with 

 various European salt dome regions. 



Eead by title. 



SOME STRUCTURAL FEATURES OF XORTH ERX IDAHO 

 BY JOSEPH B. rMPLEBY 



(Ahstract) 



The Osburn fault crosses northern Idaho and presents conclusive evidence 

 of a horizontal component of movement measurable in miles. The plane dips 

 about 65 degrees from the horizontal and, incident to movement along it, sym- 

 pathetic fractures hundreds of feet long have been opened and reopened, as 

 shown by the sequence of mineral deposition in the Coeur d'Alene district. The 

 reverse faults of the area have much less gouge than the normal ones, indicat- 

 ing that they were caused by vertical rather than horizontal stresses. These 

 stresses may have arisen from an underlying molten intrusion — a possibility 

 supported by a detailed study of the ore deposits, which, in part at least, 

 formed before the magma bed completely solidified. As the mineralization is 

 believed to have accompanied the granite intrusion on the one hand and the 

 faulting on the other, it is suggested that the great horizontal displacement 

 along the Osburn fault represents gliding on a molten subsui-face zone. 



Read in full from manuscript. 



