332 proceedings: geological society 



G. H. Ashley : The physiography of the Rockies in the Cretaceous- 

 Tertiary period. The speaker first outlined the physiographic history 

 of the region, pointing out that during Upper Cretaceous time and 

 before the Rocky Mountain region had been the scene of slow, per- 

 sistent, crustal depression, during which from 1 to 3 or more miles of 

 sediments were laid down. The period closed with movement that 

 stopped sedimentation in the Gulf area and over most of the Rocky 

 Mountain area, though sinking and sedimentation continued in the 

 center of the old basin, resulting in the laying down of the Laramie, 

 Lower Laramie, Black Buttes and possibh' Lance rocks'. Pronounced 

 uphft followed, resulting in mountain building and the subsequent ero- 

 sion that cut through the supermontane deposits and base-leveled the 

 elevated Piedmont areas. Then came a period of renewed depression 

 and sedimentation, in which were laid down the Fort Union and pos- 

 sibly Lance formations at the north and many local deposits at the 

 south, including the Raton, Denver, Puerco, Ohio Creek, Upper Lara- 

 mie, Evanston, and other associated deposits, which were derived 

 from the recently uplifted lands and overlie unconformities in the Pied- 

 mont regions but not awaj'- from the mountains. Renewed uplift and 

 erosion preceded the deposition of the Wasatch of early Eocene age. 



The position of the Lance in this physiographic outline was dis- 

 cussed in some detail from both the stratigraphic and paleontologic 

 sides, the conclusion being reached that while many facts suggest cor- 

 relation with the Laramie, and that while the formation was laid down 

 before the first mountain-uplift, the evidence as a whole strongly points 

 to the post-Laramie age of the beds. 



Comparison was then made between the ph3'siographic history of 

 this period in the Rocky ^Mountain province and that in the Gulf 

 province, the comparison seeming to show that the sea withdrawal in 

 the Gulf region corresponded to the sea withdrawal and the first period 

 of mountain building in the Rockies, and that the return of the sea in 

 the Gulf region and the laying down of the Eocene Midway and Will- 

 cox formations in that region corresponded in time with the deposition 

 in the Rock}' ^Mountain region, of the Fort L^nion, and possibly Lance 

 formations at the north and with the local sediments referred to at the 

 south, and that on that basis those formations must have been of Ter- 

 tiary age. 



Discussio7i of the papers of Hares, Heroy, and Ashley: W. T. Lee 

 spoke in confirmation of the correlation of the Mesaverde of the Lara- 

 mie Basin with the socalled Fqx Hills of the Sherman quadrangle east 

 of the Laramie ^fountains. His opinion was based on stratigraphic 

 succession and on marine fossils collected in both regions. T. W. 

 Staxtox said that as regards the correlation of the ]\Iesaverde of Lara- 

 mie Basin with the Fox Hills sandstone of Horse Creek, Wyoming, as 

 advocated by Lee and Heroy, the views expressed might possibly be 

 correct. The section at Horse Creek is obscured by overlap of the 

 White River group. The highest fossils from Cretaceous beds in the 

 neighborhood are certainly older than Fox Hills. But even if the sand- 



