CANNON BALL MARINE MEMBER OF LANCE FORMATION 539 



County, Montana. The remaining fragments are identified as 

 representing Champsosaurus, a crocodile, a turtle, and Lepisosteus. 

 Lenses of conglomerate similar to the one described above were 

 seen at other localities near the base of the Fort Union along Heart 

 River, and in one exposure a bed of conglomerate a few inches 

 thick forms the base of the formation. Along Little Missouri in 

 sec. 31, Tp. 138 N., R. 102 W., a conglomerate at the base of the 

 Fort Union contains bowlders up to a foot in diameter. The 

 unconformity shown in these exposures is such as would be 

 expected in a transition from marine to continental sedimentation. 



ROCKS or POST-FORT UNION AGE 



The rocks of post-Fort Union age in this region embrace: 

 (i) small remnants of sandstone, marl, and limestone of the White 

 River formation on the tops of a few high buttes; (2) sand and 

 gravel beds on the tops of high buttes, probably deposited by 

 streams previous to the present cycle of erosion and derived in 

 part from the White River formation; (3) terrace gravel in the 

 valleys of the larger streams from 50 to 250 feet above the present 

 valley floors ; and (4) a large number of scattered glacial bowlders, 

 the remnants of the drift of one of the earlier glacial epochs. These 

 later rocks occupy small areas and are not shown on the accompany- 

 ing map. 



INTERRELATIONSHIPS OF THE LUDLOW LIGNITIC AND THE CANNONBALL MARINE 

 MEMBERS OF THE LANCE FORMATION 



It has been shown that the Lance formation in a large region 

 immediately west of Missouri River consists of two parts, the 

 upper of which, the Cannonball member, is marine and contains 

 a fauna similar to, but not identical with, that of the Fox Hills 

 sandstone. The Cannonball member becomes gradually thinner 

 toward the west, and the sea in which it was deposited perhaps 

 did not extend as far west as the Montana line. The oyster beds 

 near Yule in Billings County, North Dakota, first discovered by 

 Leonard and later described by Stanton,^ may represent the western- 



' T. W. Stanton, "The Age and Stratigraphic Relations of the 'Ceratops Beds' of 

 Wyoming and Montana," Washington Acad. Sci., Proc, XI, (1909), 249; "Fox Hills 

 Sandstone and Lance Formation ('Ceratops Beds') in South Dakota and Eastern 

 Wyoming, Am. Jour. Sci., 4th ser., XXX (1910), 183-84. 



