278 



(including what is now known as the Torrejon). to the "Post-Cretaceous.'' 

 a group holding a position between the Cretaceous and the Tertiary. He 

 had previously assigned the Puerco to the Eocene. However, in 1887 

 (Amer. Naturalist, xxi, pp. 446. 450) he transferred this "Post-Cretacic 

 System" to what he called the Mesozoic realm. In the year 1896 Messrs. 

 S. F. Emmons, Whitman Cross and G. H. Eldridge published their "Geol- 

 ogy of the Denver Basin," in which the previously so-called Laramie in 

 the region of Denver, Colorado, was shown to consist of three distinct for- 

 mations. The name Laramie was by them restricted to the lowest mem- 

 ber of these, the succeeding formations being called respectively the Arapa- 

 hoe and the Denver. The last two had, however, already been recognized, 

 named and published by Eldridge and Cross as early as 18SS. 



Although the authors of the Geology of the Denver Basin referred to 

 the Upper Cretaceous the three formations mentioned, Whitman Cross 

 (op. cit., p. 206, seq.) makes a strong argument in favor of including the 

 Arapahoe and the Denver in the Tertiary. His plea was based especially 

 on the existence of a great stratigraphical break between the lower and 

 the middle of the three formations and on the evidence furnished by the 

 fossil plants. Certain deposits in Middle Park. Colorado ; others near 

 Canyon, Colorado ; others in the Huerfano basin ; certain ones along the 

 Animas River; still others in New Mexico, beneath the Puerco; and the 

 so-called "Ceratops" beds of Wyoming were all provisionally correlated 

 with one or other of the formations in the Denver basin. 



It is interesting, therefore, to observe that about 1S87 and 18SS, while 

 Cope was endeavoring to raise the boundary between the Mesozoic and the 

 Cenozoic to a position above what is now known as the Torrejon, Cross 

 was trying to depress it to the parting between the Arapahoe and the for- 

 mation below it 



It was thought by Cross that the beds of the Judith River valley might 

 be the equivalent of the Arapahoe beds ; but it has since been conclusively 

 shown by Stanton and Hatcher that, instead of being younger than the 

 deposits called by Cross the Laramie, the Judith beds are older than the 

 Fox Hills, older than the upper part of the Pierre. 



Within the past two years the discussion of the subjects named above 

 has again broken into flame and a number of papers have appeared, all 

 presenting most instructive facts and suggestions, but very diverse con- 



