366 W. T. LEE UNCONFORMITY IN THE SO-CALLED LARAMIE 



and are therefore of little use for correlation. The flora is not a large 

 one and is not adequate for final correlation of the beds. 



The rocks above the unconformity have yielded a flora larger than that 

 of the rocks below. From collections made by the writer in 1908, Knowl- 

 ton identified the 29 forms listed in the following table. Of these 29 

 forms, 13 are positively identified species. Nine of the 13 occur in the 

 post-Laramie of the Denver basin and only 2 in the Denver Laramie. 

 Commenting on the age of this flora, Knowlton states that it is appar- 

 ently post-Laramie and more closely related to the Denver than to the 

 Arapahoe flora, which perhaps is to be accounted for by the fact that the 

 known Arapahoe flora is very small as compared with the known Denver 

 flora. This opinion is strengthened by the known range of the species 

 previously found in the Eaton Mesa region. The existence of the two 

 coal-bearing formations has not been recognized heretofore, but judg- 

 ing from descriptions of localities from which the collections came, most 

 if not all of the 62 species of plants formerly collected in this region, 

 mainly by the geologists and paleontologists of the Hayden Survey, came 

 from the post-Laramie beds. Knowlton states that 20 of the 62 species 

 are found only in the Eaton Mesa region and can not be used for correla- 

 tion, but that 42 of them are found elsewhere. Of these 42 species 24 

 have been found in the post-Laramie formations (Arapahoe and Denver) 

 of the Denver basin, but only 3 are known from the Denver Laramie, and 

 these 3 range downward into the Montana. 



In the absence of data sufficient for the definite correlation of the beds 

 described, a choice of interpretation is left open in explanation of the 

 observed stratigraphic relations. In case all of the coal-bearing rocks 

 of the Eaton field are referred to the Laramie, as they have been up to 

 the present time, we are confronted with the fact that the "Laramie" in 

 this field contains an unconformity of considerable magnitude. By ac- 

 cepted definition the name Laramie is "restricted to the rocks conform- 

 ably overlying the uppermost marine Cretaceous (Lewis shale where 

 present) . . . the upper limit to be the first marked unconformity 

 or its stratigraphic equivalent.". It is evident either that the definition 

 is not applicable in the Eaton field or that the coal-bearing rocks are not 

 all of Laramie age. By definition the coal-bearing rocks in this field 

 below the unconformity might be either Mesaverde or Laramie, but the 

 rocks above the unconformity must be post-Laramie. If the lower forma- 

 tion be referred to the Laramie, the stratigraphic relations in the Eaton 

 field are apparently identical with those in the Denver basin, the uncon- 

 formity corresponding in time, as it does in magnitude, with the post- 



