50 



LARAMIE FLORA OF THE DENVER BASIN. 



some detail the coal measures of these areas. 

 His conclusions concerning their age wera set 

 forth as follows : 



While the evidence presented in this paper is not con- 

 sidered conclusive, and while the work upon the district is 

 not far enough advanced to warrant a final statement, yet 

 it is believed that the facts show that the coal measures of 

 the Cinnabar and Bozeman coal fields are probably of 

 Laramie age, occurring at the very base of the Laramie 

 series, and that they are conformably overlain by a totally 

 different series of rocks, composed entirely of volcanic 

 material and containing an abundant fossil flora of recog- 

 nized Laramie types, in turn overlain by beds of fresh- 

 water clays and sandstones of undetermined age but be- 

 longing to what has heretofore been considered as undoubt- 

 edly Laramie strata. 



The Livingston formation was named by 

 Weed 77 in 1893 from its typical development 

 near the town of Livingston, Mont. For the 

 decade or more preceding the publication of 

 this paper the great thickness of rocks in this 

 region above the supposed Montana Cretaceous 

 had been very generally regarded as Laramie. 

 Weed said : 7S 



Measured sections of the strata about the Crazy Moun- 

 tains show a thickness of 12,000 feet of fresh-water sand- 

 stones and clays referred to the Laramie. It is now possi- 

 ble to subdivide this great thickness of beds into Laramie, 

 a higher horizon herein named the Livingston, and the 

 still higher beds of the Crazy Mountains, which have not 

 as yet been differentiated into horizons but probably 

 represent the Fort Union beds of eastern Montana. 



It was thought by Weed and later by others 

 that "these beds present proof of a series of 

 events following the epoch of the coal-making 

 Laramie similar to those described by Whitman 

 Cross, in Colorado, of which the Arapahoe and 

 the Denver beds are the evidence." 



Weed's description of the Mesozoic section 

 began with the Jurassic, above which is what 

 he, following previous workers in the field, 

 called the Dakota, which, he said, "forms the 

 most persistent and readily recognizable horizon 

 of the Rocky Mountain Mesozoic." Above the 

 beds identified as the Dakota are over 3,000 

 feet of shales, in many places carbonaceous, 

 and interbedded sandstones, that he divided 

 about equally between the Colorado and the 

 Montana, though he stated that " a satisfactory 

 discrimination between the beds of the Colo- 

 rado and those forming this group (Montana) 



" Weed, W. H., The Laramie and the overlying Livingston formation 

 in Montana, with report on flora, by F. H. Knowlton; U. S. Geol. 

 Survey Bull. 105, pp. 1-68, 1893. 



'» Idem, p. 11. 



can not be made on paleontologic grounds, as 

 few fossils have been collected in the beds 

 assigned to the Montana." The Fox Hills was 

 not definitely recognized, though Weed said: 

 "In the eastern part of the field the dark-gray 

 sandy shales [of the Montana] are directly 

 overlain by a heavy, ledge of yellow, rather 

 dark, and very massive sandstone, which is 

 thought to be the equivalent of the Fox Hills 

 sandstone." Conformably above this is the 

 Laramie as then recognized. It is about 1 ,000 

 feet in thickness and is composed of massive 

 light-colored sandstones with intercalated shale 

 beds and coal seams. " The upper limit of the 

 Laramie in the region studied is marked by 

 an abrupt change in the composition of the 

 beds and closely resembles in general charac- 

 teristics that change which has been found so 

 prominently developed in Colorado." 



The Livingston was described by Weed as 

 follows : £ 



Overlying the coal-bearing Laramie strata there is a 

 series of beds constituting a newly recognized formation, 

 for which the name Livingston is proposed , as it is typically 

 developed in the vicinity of Livingston. This formation 

 consists of a series of beds, in places aggregating 7,000 feet 

 in thickness, composed of sandstones, grits, conglomerates, 

 and clays, made up very largely of the debris of andesitic 

 lavas and other volcanic rocks and including local inter- 

 calations of volcanic agglomerates. 



The Livingston formation was believed by 

 Weed to rest unconformably on the Laramie, 

 and the basis for this belief was set forth at 

 length in the paper under consideration. The 

 upper part of the Livingston was said to pass 

 without observed stratigraphic break into the 

 overlying beds then presumed and since proved 

 to belong to the Fort Union formation. 



The fossil plants of the Bozeman coal field 

 and adjacent areas were considered by me in 

 Weed's report above cited, 79 in a more formal 

 presentation of the facts published the pre- 

 ceding year. 80 The fossil flora, as then known, 

 embraced 44 species, and the conclusion was 

 reached that the plants from the coal-bearing 

 beds belong " to what is generally known as the 

 Laramie," while "the flora of the Livingston 

 formation finds its nearest relationship with the 

 flora of the Denver beds of Colorado." 



™ Knowlton, F. H., Annotated list of the fossil plants of the Bozeman, 

 Mont., coal field, with table of distribution and description of new 

 species: U. S. Geol. Survey Bull. 105, pp. 43-66, pis. 5, 6, 1893. 



80 Knowlton, F. H., The fossil flora of the Bozeman eoal field: Wash, 

 ington Biol. Soc., vol. 7, pp. 153, 154, 1892. 



