104 



LARAMIE FLORA OF THE DENVER BASIN. 



signed to the Laramie in this area was about 

 1,600 feet. The crucial point is the disclosure 

 of the Arapahoe conglomerate between the two 

 coal horizons, which naturally tends to decrease 

 the observed thickness of the Laramie strata. 



The other supposed locality for Arapahoe 

 plants — namely, that near the Douglas coal 

 mine, west of Sedalia — may now be considered. 

 As this is at or near the type locality for the 

 Arapahoe there should apparently be no ques- 

 tion as to its relation, but it appears from the 

 work of G. B. Richardson, who critically stud- 

 ied this area in 1910-11, that the Arapahoe 

 occupies the stratigraphic position of the Daw- 

 son arkose and in fact interdigitates with the 

 lower part of it. Concerning this point Rich- 

 ardson " wrote as follows : "It was found that 

 the lower part of the Dawson arkose seems to 

 pass along the strike into the Arapahoe and 

 Denver formations; that the Dawson and 

 Arapahoe can not be separated lithologically, 

 even at the type locality of Arapahoe, on the 

 bluffs of Willow Creek." This conclusion does 

 not, of course, affect the stratigraphic relations 

 of the plant-bearing beds, and it is unimportant 

 whether the beds are to be called Arapahoe or 

 Dawson, as they are separated from the under- 

 lying Laramie by an unconformity marking a 

 considerable time interval. 



Below is a tentative list of the plants from 

 the Douglas mine locality as worked up about 

 12 years ago. Additional material not yet 

 studied may necessitate slight changes, though 

 it is not presumed that these will greatly affect 

 the result. 



Acer trilobatum productum. 



Asplenium erosum. 



Berchemia multinervis. 



Cissus laevigata. 



Ciesus lobato-crenata. 



Dicksonia, new. 



Diospyros brachysepala? 



Dombeyopsis obtusa. 



Dombeyopsis, new. 



Dryopteris lakesii. 



Dryopteria lesquereuxii? 



Ficus planicostata. 



Ficus, new. 



Hicoria? sp. 



Laurus primigenia. 



Nelumbo lakesii. 



Nelumbo, new. 



Phyllites, new. 



Quercus, new. 



n Bichardson, G. B., The Monument Creek group: Geol. Soe. America 

 Bull., vol. 23, p. 274, 1912. 



Viburnum, new. 

 Woodwardia latiloba. 



It will be seen at once that this is essentially 

 a Denver flora, with only two species tiiat 

 occur in the Laramie— Dombeyopsis obtusa and 

 Ficus planicostata. Both of these species have 

 already been several times mentioned as passing 

 from Laramie into post-Laramie beds. 



RELATIONS TO THE LANCE FORMATION. 



It is difficult at present to make an accurate 

 and wholly satisfactory comparison between 

 the flora of the Laramie in the Denver Basin 

 and the flora of the Lance formation. This 

 difficulty arises from the fact that the Lance 

 flora has not yet been thoroughly worked up 

 and described. It is known that the Lance 

 "flora comprises approximately 125 forms. It 

 is possible that when this flora has been fully 

 described, the number of species found to be in 

 common with the Laramie may be slightly 

 increased over the number given below, but it 

 is improbable that they will be increased to as 

 many as twice that number. Another diffi- 

 culty in the way of making an accurate com- 

 parison between these two floras is the uncer- 

 tainty that still attaches t6 certain of the locali- 

 ties that have afforded some of the supposed 

 Lance plants. It is perhaps unnecessary to 

 state that there has been — and indeed still is — 

 more or less uncertainty in fixing the limits 

 of the Lance formation, though the difficulty is 

 much greater in fixing the upper limit than it is 

 in fixing the lower limit. Be this as it may, 

 the species mentioned below are the only ones 

 that are at present recognized as passing from 

 the Laramie into the Lance. 



Equisetum perlaevigatum. 

 Myrica torreyi. 

 Ficus planicostata. 

 Cinnamomum affine?? 

 Rhamnus salicifolius. 

 Flatanus platanoides. 

 Quercus viburnifolia? 



A discussion of these species may be of 

 interest. Thus, Equisetum laevigatum (now 

 perlaevigatum) was reported by Hollick from 

 the so-called "Hell Creek beds" (Lance) in, 

 the vicinity of Hell Creek, Mont. In the de- 

 scriptive part of this paper (p. 113) it is stated 

 that this species was founded on two speci- 

 mens, one of which (from Sand Creek, Colo., 

 in beds now believed to be of Denver age) is 



