THE LARAMIE FLORA OF THE DENVER BASIN, 



WITH A REVIEW OF THE LARAMIE PROBLEM. 



By F. H. Knowlton. 



INTRODUCTION. 



In the investigation of the Laramie flora 

 which I began about 1889 it was my original 

 intention to study the flora of the Laramie 

 formation of the entire Rocky Mountain region, 

 over which the formation was then understood 

 and generally accepted as being widely dis- 

 tributed. As a preliminary to this study the 

 older collections, which had served as the 

 basis for the work of Lesquereux, Newberry, 

 and others, were critically reviewed. To this 

 basis was to be added the new material that 

 was becoming available in ever-increasing 

 volume. It very soon became evident, how- 

 ever, that opinion concerning the Laramie for- 

 mation was undergoing a transition, during 

 which, as will be shown in the historical review 

 which follows, area after area was found to 

 have been incorrectly or unwisely assigned to 

 the Laramie. The work was consequently de- 

 layed pending the settlement of these disputed 

 points, and subsequent events have abundantly 

 proved the wisdom of postponement, for other- 

 wise the result would have been a composite 

 picture and open to the same objections as 

 those that fall upon Ward's "Flora of the 

 Laramie group." The revision of the older 

 material, together with the descriptions of 

 such new material as came to hand from time 

 to time, has consequently lain in manuscript 

 for many years, though it has been available 

 and has furnished the basis for numerous ten- 

 tative considerations of this flora. 



In view of the uncertainties as to the ultimate 

 classification of certain of the supposed Laramie 

 areas, it was finally decided to restrict this ac- 

 count to an area about which there is little or no 

 disagreement. The Denver Basin in Colorado 



offers such an area. The geologic relations of 

 the Laramie as understoo'd in 1895 were set 

 forth by Emmons, Cross, and Eldridge in their 

 monograph on the geology of the Denver Basin.' 



After the segregation of the Arapahoe and 

 Denver formations from the Laramie, there re- 

 mained the Laramie unit as now accepted, 

 which is believed to fulfill in all essential par- 

 ticulars the requirements of the original defini- 

 tion by King. When the Denver Basin mono- 

 graph was published, it was supposed that the 

 coal-bearing Laramie rocks were present 

 throughout the Front Range. Subsequent 

 study has shown, however, that the Laramie is 

 not now known to extend beyond Colorado 

 Springs on the south. 



This paper deals with the plants known from 

 the Laramie of the Denver Basin, which is here 

 considered as slightly larger than the limits set 

 in the monograph above mentioned, extending 

 from the vicinity of Greeley to the divide near 

 Palmer Lake on the south. The southernmost 

 exposure of Laramie rocks in the Castle Rock 

 quadrangle is in practical continuity with the 

 Laramie in the Denver Basin and is separated 

 by a covered interval of only about 18 miles 

 from the nearest exposure of Laramie in the 

 Colorado Springs quadrangle. To the east the 

 Laramie extends for varying distances out on 

 the plains, where, however, it is more or less 

 deeply covered by the Arapahoe or Denver 

 formations or the Dawson arkose. 



The material on which this paper is based 

 was derived from many sources. Most of the 

 original material on which Lesquereux based 

 his studies is preserved in the United States 

 National Museum and has been freely con- 



1 U. S. Geol. Survey Mon. 27, 1896. 



