proceedings: geological society 157 



G. R. Mansfield and P. V. Roundy: Some Jurassic and Cretaceous 

 formations of southeastern Idaho. (Illustrated.) 



In the Montpelier and Wayan 30-minute quadrangles of south- 

 eastern Idaho parties of the Geological Survey have found great thick- 

 nesses of strata, aggregating 17,000 feet or more, that have hitherto 

 been assigned to the Beckwith and Bear River formations. On the 

 maps of the Hayden Surveys both formations are included in the 

 Laramie. The Beckwith has been assigned to the Cretaceous or Juras- 

 sic, and the Bear River to the Upper Cretaceous. There is such 

 lack of agreement between the formations in the quadrangles named 

 and the Beckwith and Bear River formations in their type localities 

 that it now seems inadvisable to continue the use of the names Beck- 

 with and Bear River in this district. Three groups of strata are recog- 

 nized, the lowest of which is marine Jurassic and rests unconformably 

 upon the Twin Creek limestone, the main Jurassic formation of the 

 region. The two higher groups are non-marine and probably Lower 

 Cretaceous. They are separated from each other by an unconformity, 

 but the lower group appears to be conformable on the Jurassic beds 

 below. The two higher groups have some resemblances to the Koo- 

 tenai, but the data are at present insufficient for their correlation with 

 that formation. No characteristic Bear River fossils have been found 

 in the district, though such have been found farther north, and there 

 is a possibility that the doubtful beds may grade upward into the true 

 Bear River in that direction. The beds formerly called Beckwith 

 are divided into seven formations and a new name is given to the strata 

 hitherto called Bear River. The paper gives a statement of the strati- 

 graphic problems involved, together with a description of the formations. 



Discussion. C. J. Hares asked if the pebbles of the conglomerate 

 described could be attributed definitely to any older formation. Mans- 

 field replied that many different formations were probably represented 

 but could not be definitely recognized. T. W. Stanton remarked on 

 the lithologic and successional differences in this section from those 

 in adjacent sections. He said also that the formations between the 

 marine Upper Jurassic and the marine Upper Cretaceous still needed 

 much study before it would be possible to make definite correlations. 



A. C. Spencer: Gold deposits of the Atlantic and South Pass Dis- 

 tricts, Wyoming. (No abstract.) 



At the 301st meeting, held December 8, 1915, the presidential ad- 

 dress was delivered by the retiring president, T. Wayland Vatjghan: 

 Some problems in the geologic history of the perimeters of the Gulf of Mexico 

 and. the Caribbean Sea. The address will be published at a later date. 



At the twenty-third annual meeting the following officers were elect- 

 ed for the ensuing year: President, Arthur C. Spencer; Vice-Presi- 

 dents, W. C. Mendenhall and F. H. Knowlton; Secretaries, Carroll 

 H. Wegemann and H. E. Merwin; Treasurer, S. R. Capps; Members-at- 

 large of the Council, B. S. Butler, C. W. Gilmore, G. F. Loughlin, 

 H. S. Gale and R. W. Pack. C. N. Fenner, Secretary. 



