540 E. RUSSELL LLOYD AND C. J. HARES 



most limit to which the Cannonball sea extended. This region was 

 studied in 191 1, and it was found by Hares that the beds containing 

 the oysters are about 700 feet above the base of the Lance. 



The zone in which Ostrea glabra and Ostrea suhtrigonalis occur, 

 in Tps. 136, 134, and 134 N., R. 105 W., is considered the westward 

 extension (so far as known at present) of the strata of marine origin, 

 as the oysters are brackish-water animals and consequently must 

 have had some connection with the open sea. The most westerly 

 collection of the Cannonball marine fauna is only 30 miles east of 

 this place, in sec. 21, Tp. 129 N., R. 100 W., 4 miles west of Haley, 

 and occurs stratigraphically within 100 feet of the T Cross lignite 

 bed which was traced from Tp. 134 N., R. 105 W., to the west 

 side of Tp. 129 N., R. loi W. The oysters occur about 70 feet 

 above the same lignite bed; it is assumed that the seaward con- 

 nection was to the east. The oysters also occur about 120 feet 

 below the base of the Fort Union formation which in the Little 

 Missouri region has the same characteristics (channel conglomerate, 

 light-yellow, somewhat massive sandstone) as it does in the Cannon- 

 ball River country where it rests directly on the Cannonball marine 

 member. It appears that the sea in which were deposited some 

 300 feet of marine sediments transgressed westward across' the 

 lignitic strata of the Ludlow member and that the position of its 

 westward limit is underneath the divide between the drainage of 

 Little Missouri and that of Grand and Cannonball rivers. All 

 of the Triceratops collected in the Little Missouri country came 

 from below the T Cross lignite bed and the oysters from above 

 it. Calvert, however, states that in Montana "Ceratopsian bones 

 were found just above the lowest persistent lignite bed, but there 

 is certainly nothing in the character of the overlying strata to sug- 

 gest that similar bones do not occur therein up through a strati- 

 graphic distance of perhaps 500 feet."^ The T Cross lignite bed 

 was mapped to the Montana state line and it is undoubtedly the 

 same lignite as the ''persistent lignite" referred to above. 



The presence of numerous lignite beds in the upper part of the 

 Ludlow lignitic member of the Lance is in strong contrast to the 



^ W. R. Calvert and Others, "Lignite in Eastern Montana," U.S. Geol. Survey 

 Bull. 4^1, p. 197, 1912. 



