paleontological geology 
65 
identified except one form from the Union beds. The conclusion 
is reached that the Cannonball marine beds, and consequently the 
whole of the Lance formation are Cretacic in age. 
Among the 60 molluscan forms 33 are regarded as new; and 
27 are identified with previously d 7 scribed species. Eighteen of 
the species are found in the Fox Hills formation. Twelve of the 
forms occur in the Pierre shales. To the westward, in the Rocky 
Mountains, six species are found in the Bear Paw beds of the 
Pierre; and three species appear in the Laramie brackish-water 
beds. One) form was previously taken in the basal layers of the 
Union terrane. 
It is evident that a large element in the Cannonball fauna is 
directly descended without specific modification, or with only 
slight change, from the preceding Cretacic faunas of the Rocky 
Mountains and Great Plains regions. These Late Cretacic faunas 
display progressive modernization due to the gradual elimination 
of distinctive Mesozoic types and the concurrent introduction of 
modern generic forms which continued through the Tertiary times 
and are still living. 
The Cannonball fauna is really a Fox Hills fauna from which 
certain characteristic Cretacic types have disappeared, and which 
was farther modified by the immigration of a number of other 
types that were not present in the Fox and Pierre seas of the 
Great Plains region. 
Stanton. 
Lance and Union Formation are Mesozoic in Age. In the 
Black Hills region paleogeographical maps bring out the fact that 
the Cannonball terrane is a product of the final Cretacic seas, 
since there is no possibility of connecting this marime section with 
any of the Gulf Eocene, or the Eocene of the Pacific coast. It is 
therefore the marine equivalent of the Lance formation. 
Inasmuch as the Lance and Union sections are continuous 
formations, have wholly archaic mammalian faunas, and are broken 
by a period of orogeny and lack of deposition from the succeeding 
Eocene deposits, with their entirely different and modernized 
mammals, the line of separation between the Mesozoic and Ceno- 
zoic apparently lies between the Union and Wasatch formations 
and not between the Fox and the Lance beds. 
