282 H. T. Hill — North American Cretaceous History. 



assigned by Mr. Hills to the Eocene though no fossil remains 

 have yet been determined. Above these beds are still others, as- 

 signed provisional^ to the Pliocene. 



The present article is intended to present some facts estab- 

 lished in a special work. But the facts have a more or less 

 direct value in considering many of the important problems of 

 Rocky Mountain geology. Some of these questions have been 

 hinted at in discussing the age of the Denver Formation, but a 

 further development of the bearings of the facts stated is a 

 task requiring a wide experience in various fields, and this 

 presentation I gladly leave to my chief, Mr. S. F. Emmons, 

 who will give a broader treatment of the subject in the mono- 

 graph upon the Denver Basin. My sincere thanks are due to 

 Mr. Emmons for his kindness and courtesy in approving the 

 publication of this article. 



Note. — Mr. Eldridge has recently ascertained that the name " Willow Creek" ' 

 has already been applied to several local Formations in this country, and he has 

 therefore decided to call the Formation between the Laramie and the Denver the 

 Arapahoe instead of the Willow Greek. This decision was reached too late to 

 allow of correction in the body of the above article. Arapahoe is the name of 

 the county in which the city of Denver is situated, and the beds in question are 

 there very prominently developed. — W. C. 



Akt. XXX. — Events in North American Cretaceous History 

 illustrated in the Arkansas- Texas Division of the South- 

 western Region of the United States •* by Robt. T. Hill. 



During the last two years the writer has been permitted 

 by the joint effort of Dr, John C. Branner, State Geologist of 

 Arkansas, and the Director of the United States Geological 

 Survey to investigate the stratigraphic and paleontologic con- 

 ditions of the northern and eastern termination of the Texas 

 Cretaceous, and to trace out its detailed relations to those of 

 the Gulf and western states with their accompanying phe- 

 nomena. The condition of knowledge previous to that time 

 was fully set forth in this Journal for October, 1887. From 

 later investigations I am able to present the following brief 



* The southwestern region of the United States maybe defined in stratigraphic 

 terms as those portions of Arkansas, Texas, Indian Territory, southern Kansas, 

 New Mexico and Arizona, south of the Uinta and Ozark uplifts and between 

 the Sierras on the west and the great Atlantic timber belt on the east. Its 

 principal divisions are the Arizona-Utah or Grand Canon; the Rocky Mountain 

 or New Mexican ; the West Texan or Permo-Triassic ; the Central Texas Paleo- 

 zoic: and the eastern or Arkansas-Texas Cretaceous division lying between 

 the last and the western borders of the Tertiary strata of the Mississippi embay- 

 ment, as laid down upon Hitchcock's Geological Map of the United States. 



