92 



LARAMIE FLORA OF THE DENVER BASIN. 



Popes Bluff, west pf Pikeview, Colo.; collected by A. C. 

 Peale and M. I. Goldman, 1908: 



Pteris goldmani Knowlton, n. sp. 



Cyperacltes? tessellata Knowlton, n. sp. 



Sabal sp. cf . S. montana Knowlton? 



Smilax? inquirenda Knowlton, n. sp. 



Juglans praerugosa Knowlton, n. sp. 



Juglans laramiensis Knowlton, n. sp. 



Myrica dubia Knowlton, n.sp. 



Picus arenacea Lesquereux. 



Ficus denveriana? Cockerell. 



Ficus cockerellL Knowlton, n. name. 



Ficus navicularis Cockerell. 



Ficus planicostata Lesquereux. 



Cinnamomum affine Lesquereux. 



Rhamnus salicifolius Lesquereux. 



Rhamnus sp. 



Zizyphus coloradensis Knowlton, n. sp. 



Dombeyopsis obtusa Lesquereux. 

 Opposite sand-lime brick works, Pikeview, 4 miles 

 north of Colorado Springs, Colo.; collected by A. C. Peale, 

 1908 [No. 24]: 



Anemia sp. 



Ficus arenacea? Lesquereux. 



Ficus navicularis Lesquereux. 



Ficus sp. 



Cinnamomum affine? Lesquereux. 



Rhamus salicifolius Lesquereux. 



Dombeyopsis trivialis? Lesquereux. 



Leguminosites laramiensis Knowlton, n. sp. 

 - Crow Creek, about 25 miles northeast of Greeley, Colo.; 

 collected by F. H. Knowlton and T. W. Stanton, 1896: 



Sequoia acuminata Lesquereux. 



Myrica* torreyi Lesquereux. 



Platanus platanoides? (Lesquereux) Knowlton. 



Dombeyopsis obtusa Lesquereux. 



DIFFICULTIES IN THE STUDY OF THE EARLIER 

 COLLECTIONS. 



Much difficulty has been experienced in 

 studying the older collections from this region. 

 For many years it was not supposed to be 

 necessary to give more than a very general 

 locality label — such as "Golden, Colo.," "near 

 Denver, Colo.," as it was presumed that all 

 the plant-bearing beds were of the same age. 

 At first the age was given as "Lignitic" or 

 " Colorado Lignitic," and later all the specimens 

 were referred to the Laramie without distinc- 

 tion. However, when it was later demon- 

 strated that two or even three distinct plant- 

 bearing formational units may be present in 

 the same section, confusion became con- 

 founded. It was the fusion pf horizons, here 

 and elsewhere, that for so long a time obscured 

 and negatived any results that could be ob- 

 tained by a study of the flora. Consequently, 

 after the segregation of the Arapahoe and 

 Denver formations from the Laramie, it 



naturally became of the greatest interest and 

 importance to ascertain the extent to which 

 the fossil flora confirmed this differentiation of 

 horizons. 



In the absence of original labels or other 

 data by which the plants can be connected 

 with a definite locality or horizon, there appear 

 to be only two methods by which their posi- 

 tion can be arrived at — (1) by a study of the 

 lithologic characteristics of the matrix con- 

 taining the fossils, or (2) by the collection of 

 additional specimens from beds of known 

 position. When Whitman Cross 5 established 

 the Denver formation he recognized at once 

 the necessity for making an examination of 

 this kind, and consequently he made a careful 

 study of the matrix of such of the Golden 

 plants as were then available. Fortunately, 

 nearly 90 per cent of the specimens on which 

 Lesquereux based his work are preserved in 

 the collections of the United States National 

 Museum, and by studying the matrix of each 

 species Cross was able to arrive at valuable 

 results. As is now known, it is comparatively 

 easy to distinguish between the quartzose 

 sandstone of the Laramie and the peculiar 

 yellowish-brown andesitic material of the 

 Denver. 



This study by Cross was confined to the 

 plants from Golden enumerated by Lesquereux 

 in his "Tertiary flora" and "Cretaceous and 

 Tertiary floras." These works together de- 

 scribe just 100 species from this locality, 

 hence numbers express percentages. Cross 

 was then able to find 79 species, of which he 

 says: 



Eighteen occur in what is judged to be Laramie sand- 

 stone or shale, and 59 in distinct Denver beds of Table 

 Mountain, while 7 occur in both rocks, and 9 cases are in 

 doubt. Lesquereux gives horizons for 6 species that were 

 not found. By combining these two sources of informa- 

 tion we get probable indications for 76 per cent of the 

 Golden fossil plants; 22 per cent came from true Laramie 

 strata and 63 per cent from Table Mountain beds; 9 per 

 cent occur in both formations. 



A few years later Lesquereux 6 published a 

 short paper entitled "Fossil plants collected 

 at Golden, Colo.," in which he added 60 

 species to this flora. There is no mention in 

 this paper of a definite horizon or of an exact 



s The Denver Tertiary formation: Am. Jour. Sci., 3d ser., vol. 37, pp. 

 272-275, 1889. 



• Lesquereux, Leo, Harvard Coll. Mus. Cbmp. Zoology Bull., vol. 16, 

 pp. 43-59, 1888. 



