356 B. BROWN CRETACEOUS-EOCENE CORRELATION IN NEW MEXICO 



I have determined tlie geologic sequence in each of these formations 

 and the succession of the species of reptiles. The mammals have been 

 determined with the aid of Dr. W. D. Matthew, the invertebrates with the 

 aid of Dr. T. W. Stanton, the flora with the aid of Dr. F. H. Knowlton 

 and Dr. A. Hollick. 



In this contribution to the present discussion as to what we shall con- 

 sider the close of Cretaceous and opening of Eocene time in Xorth 

 America, I desire to add certain hitherto unpublished observations and 

 to review observations already in print bearing on this important 

 question. 



In 190T I published in the Amerirnn Museum Bulletin an article on 

 the Hell Creek beds of Montana, ^vith lists of fauna and flora known up 

 to that time. In 1908 and 1909 I continued work in the Hell Creek 

 region, searching for fossils along the eastern exposure of the l>eds, and 

 considerably increased the faunal list of the section. 



Formations correlated with the Lance are indicated in quotation marks, 

 thus, "Lance." It is vers- confusing to omit these quotation marks. 

 The ^Tjance" formation should be known faunally as the Triceratops 

 Zone. The application of the term '^Ce rat ops Zone" or "Ceratops Beds" 

 to this formation is absolutely erroneous and misleading because the 

 genus Ceratops became extinct long before "'Lance'' times and is dis- 

 tinctive of the much more ancient Judith River or Belly River 

 formations. 



The Hell Creek and the typical Lance are the only formations which 

 may now be absolutely correlated with each other by all the species of 

 plants and animals which they contain. It is best, therefore, to first 

 consider the Hell Creek. 



Hell Creek Formation, ^Iontana 



The notes on this section relate to the contact of the marine Fox 

 Hills and the overlying '"Lance" (Hell Creek beds). 



Whatever the character of the Fox Hills formation may be in other 

 localities, it is here clearly differentiated from the Pierre in lithologic 

 structure. The partition plane separating the Fort Pierre and Fox 

 Hills is the junction of the dark shales of the fonner, with the grayish- 

 yellow sandy shales and sandstones of the latter. The formation is not 

 extensively developed, and is here never more than 100 feet thick. It 

 consists of arenaceous shales and soft, friable sandstones, with an in- 

 creasing amount of sandstone toward the top. in marked contrast to the 

 dark shales of the Pierre l>elow. The sandstones are frequently rendered 

 impure by more or less argillaceous material. In the exposures on Hell 



