32 CROSS 



marine Cretaceous, and thus corresponding to the principal element 

 of King's definition, and an upper portion exhibiting relations at 

 variance with that definition. With the recognition of the Arapahoe 

 and Denver formations, separated in time from the Laramie of the 

 conformable series by an epoch of uplift and great erosion, came the 

 necessity of revising the application of the term Laramie. The 

 Arapahoe and Denver beds were at first considered to be the earliest 

 deposits of the Eocene series.*" Taking them from the Laramie 

 made no change, I think, in the definition of the latter as the upper- 

 most member of the conformable Cretaceous series in the Rocky 

 Mountain region, although Mr. Veatch considers it "redefinition." 



Soon after the recognition of the Arapahoe and Denver forma- 

 tions other deposits of nearly synchronous origin were discovered in 

 discordant relations with the Cretaceous section, a notable instance 

 being the Livingston beds of Montana. It was also found by Marsh 

 and Hatcher that the horned dinosaurs and associated vertebrates, 

 the so-called "Ceratops fauna," occurred in Converse County, 

 Wyoming, in strata which appeared to occupy the position of the 

 Laramie, in conformity with the marine Cretaceous. The presence 

 of the same fauna in the Arapahoe and Denver beds led many geolo- 

 gists and paleontologists to the belief that the latter must also be of 

 Cretaceous age, and that the breaks below the Arapahoe and Liv- 

 ingston beds were of local importance. 



In 1892 I reviewed the accumulated evidence concerning the 

 importance of the Arapahoe and Denver beds and deposits correlated 

 with them by. virtue of unconformity or fossil evidence and in con- 

 clusion advocated: — 



"The restriction of the term Laramie, in accordance with its 

 original definition, to the series of conformable beds succeeding the 

 marine Montana Cretaceous, and the grouping of the post-Laramie 

 lake beds described, with their demonstrated equivalents, in another 

 series to which a comprehensive name shall eventually be given."'' 



This course had previously been proposed by R. C. Hills.'^ In 



'"Cross, Whitman: The Denver Tertiary Formation. Amer. Jour. Sci., 

 (3), Vol. XXXVII, 1889, pp. 261-282. 



" "Post-Laramie Deposits of Colorado." Amer. Jour. Sci., (3), Vol. XLIV, 

 1892, p. 41. 



" Orographic and Structural Features of Rocky Mountain Geology. Proc. 

 Colo. Sci. Soc, Vol. Ill, 1890, p. 397. 



