proceedings: geological society 295 



the mouth of the Medicine Bow." The author, assisted by Dr. A. C. 

 Peale, visited the area in 1910 and failed to find a trace of remains of 

 dinosaurs in the "Lower Laramie," but did find Triceratops in place 

 300 feet above the base of the "Upper Laramie," or Lance formation as 

 it must now be called. This discovery is regarded as of far-reaching' 

 importance, since it proves that the Lance formation ("Ceratops beds"), 

 which elsewhere rests on Fox Hills and other Montana formations, is 

 here above a great unconformity which separates it from the 6500 feet 

 of "Laramie" and effectually disposes of the contention that the Lance 

 formation is the equivalent of the Laramie. 



An area in South Dakota west of the Missouri River and between the 

 Cannonball and Cheyenne Rivers, was studied in 1909 by parties from 

 the U. S. Geological Survey under the general charge of W. R. Calvert, 

 who furnished the data for this part of the paper. The four formations 

 present in this region are Pierre, Fox Hills, Lance and Fort Union. The 

 Fox Hills with a maximum thickness of 150 to 200 feet, has been irregu- 

 larly reduced by erosion and in exceptional instances has been entirely 

 removed. The Lance formation rests on the eroded surface of the Fox 

 Hills and in at least one locality upon the Pierre. Angular as well as 

 erosional discordance has also been noted between them, especially on 

 the Moreau River near Go vert P. O., where the Fox Hills dips at an 

 angle of 10° and the overlying Lance is horizontal. The marine Fox 

 Hills invertebrates, reported at five localities in the basal 10 or 12 feet 

 of the Lance formation, are presumed to be re-deposited, as they always 

 occur in eroded channels. 



Converse County, Wyoming, the type locality for the Lance formation, 

 has been visited by several parties and the attempt made to fix the upper 

 line of the Fox Hills, but while it appears that these beds are of unequal 

 thickness, the fact remains that the upper limit is not yet definitely 

 placed. 



In southeastern Montana the relations between the Fox Hills and the 

 overlying Lance formation were found to be the same as already shown 

 for South Dakota, that is, they are separated by an unconformity which 

 is erosional and occasionally also angular. 



In the original paper the statement was made that thruout the vast 

 region studied the Lance formation was found conformably overlain by 

 the acknowledged Fort Union. Field work of the past two seasons 

 has confirmed this in every particular, and there is yet to be observed a 

 single locality at which unconformable relations have been even sus- 

 pected. Hence it seems to have been demonstrated that sedimentation 

 from one to the other was continuous and uninterrupted. 



The following conclusions regarding the stratigraphic relations of the 

 Lance formation seem justified: (1) The Lance formation is separated 

 from the underlying formations by an unconformity, which in some 

 cases at least is profound; (2) the Lance formation is not the equivalent 

 of the Laramie, in fact, as shown by the relations in Carbon County, 

 Wyoming, they are separated by a great unconformity; (3) the Lance 

 formation cannot be separated on structural or lithologic grounds from 



