proceedings: geological society 431 



ber of the Mesaverde, as mapped in central Wyoming, and is also 

 present in the southern part of the Bighorn Basin. The Judith River, 

 as traced southward, includes the lower part of the Meeteetse formation 

 and corresponds to the upper part of the Mesaverde of central and 

 southern Wyoming. The Bearpaw shale can be recognized as a marine 

 shale as far south as Elk Basin, and marine sandstones are recognized 

 as far south as the Shoshone River and Grey bull. Further detailed 

 mapping will probably establish the fact that the Bearpaw corresponds 

 in whole or in part with the Lewis shale of the southern areas. The 

 work also shows that the formations as a whole are thinner in the north- 

 ern and central Wyoming areas. Apparently the source of sediments 

 was chiefly from the west or southwest direction. This is borne out 

 in part by the fact that on the west side of the Bighorn Basin no purely 

 marine beds are present above the base of the Mesaverde. 



Discussion: C. F. Bowen spoke of the feathering of the Eagle sand- 

 stone near the Musselshell River. C. H. Wegemann said that about 

 30 miles southeast of Billings the Eagle sandstone disappears among 

 shales. T. W. Stanton called attention to the almost perfect corre- 

 lation which recent detailed study had made possible. 



Willis T. Lee : Relations of the Morrison and Sundance formations. 

 Sedimentary rocks of variable character and thickness, belonging to the 

 Sundance formation (marine Jurassic) occur in most places along the 

 eastern foothills in Colorado as far south as Morrison, where they are 

 10 to 20 feet thick. They have heretofore been included in the Morri- 

 son formation but are now known to lie unconformably below the low- 

 est dinosaur beds. These Jurassic rocks lie unconformably on Per- 

 mian red beds (Lykins). Farther to the south, beds of gypsum, now 

 referred to the Lykins, may in fact represent the horizon of the marine 

 Jurassic. The Morrison formation rests unconformably on the Jur- 

 assic, or on the Permian where the Jurassic is absent. In the upper 

 part of the Morrison at the type locality of this formation a small 

 collection of fossil plants, which F. H. Knowlton has determined to 

 be highly developed dicotyledons of Cretaceous age, was obtained. 

 Although the plants were found above the highest known dinosaur 

 horizon, no question has been raised as to the propriety of including 

 the plant horizon in the Morrison formation, nor is it probable that 

 any geologist familiar with the section in the field will raise such a 

 question unless he discards the accepted definition and redefines the 

 formation. These rocks, together with the dinosaur beds a few feet 

 lower, were once classed as Jurassic because of the supposed Jurassic 

 affinities of the dinosaurs; later as "Jurassic or Cretaceous;" and finally 

 as "Lower Cretaceous (?)." The plants recently found are of such 

 character as to place the rocks containing them definitely in the Cre- 

 taceous and at a horizon considerably above the base of the system. 

 As the Dakota sandstone, usually classed as basal Upper Cretaceous, 

 occurs above the rocks containing the plants, it is appropriate to class 

 those between it and the Jurassic as lower Cretaceous. The Morrison 

 formation has been regarded as a stratigraphic unit although probably 



