CANNONBALL MARINE MEMBER OF LANCE FORMATION 533 



Generalized Section along North Fork op Grand River between 

 Bloom, South Dakota, and Haley, North Dakota^ 



Ft. In. 



1. Sandstone, brown and yellow, fine-grained, thin-bedded, and 



lenses of limestone 30 o 



2. Sandstone, marine; burrows of a Teredo-like shell, Anchura 



americana 10 o 



3. Shale I o 



4. Lignite 2 o 



5. Shale and sandstone, interbedded. Sandstone in lower 

 part, light brown, medium fine-grained, micaceous; con- 

 taining Halymenites major, Thracia sp., Nucula sp., 

 Callista sp., Pholas sp., imprints of pelecypods and shark 



teeth 40 o 



6. Lignite i o 



7. Shale 4 o 



8. Lignite 2 3 



9. Shale 



90 3 



Note. — ^No. i was considered Fort Union but may be Cannonball; Nos. 2 and 

 part of 5 are marine, and Nos. 3, 4, 6, 7, 8, and 9 are considered fresh-water. 



Cannonball marine member. — The Cannonball marine member of 

 the Lance formation has been traced and mapped in an area extend- 

 ing from near Mandan, North Dakota, to the vicinity of Ralph 

 post-oii6ice in Harding County, South Dakota, and 4 miles west of 

 Haley, Bowman County, North Dakota. The presence of brackish- 

 water fossils, Ostrea glabra, near Yule on Little Missouri River in 

 BiUings County, North Dakota, shows that the sea probably 

 extended some distance farther to the west than its sediments, have 

 been mapped. The extent of this member east of Missouri River 

 is unknown. 



The marine member is composed predominantly of dark sandy 

 shale or shaly sandstone with a subordinate amount of dark- 

 yellow and gray sandstone. It also contains some thin limestones. 

 All the strata are lenticular in character and individual beds can be 

 followed for only short distances. The member is typically exposed 

 in the bluffs of Cannonball River in Tps. 132 and 133 N., Rs. 87 

 and 88 W. The following sections measured in the type area show 



' The last three sections expose the interrelations of the Ludlow lignitic and the 

 Cannonball marine members. 



