64 



the paper by Stanto 

 mentioned : 



LARAMIE FLORA OF THE DENVER BASIN. 



and Knowlton already 



The most prominent feature of the section at Black 

 Buttes is the massive bed of sandstone, somewhat over 100 

 feet thick at the base of the exposure, forming steep hills 

 and cliffs northeast of the railroad opposite the station and 

 passing beneath the surface by its dip of 9° or 10° near the 

 coal mine. The upper portion of it is also exposed on the 

 south side of Bitter Creek valley, about a mile from the 

 station . All of the Laramie fossils , whether plants , inverte- 

 brates, or vertebrates, that have hitherto been described or 

 listed as coming from Black Buttes were obtained from the 

 overlying beds within about 100 feet of the top of this mas- 

 sive sandstone. The original specimen of Agathaumas 

 sylvestris was found about 20 feet above it, and the plants 

 that have been described came from the same horizon and 

 from several higher bands up to the bed overlying the prin- 

 cipal coal, some 60 or 75 feet higher. The invertebrates from 

 this locality have about the same range. • Most of the beds 

 vary considerably in character and thickness within short 

 distances; but the fossiliferous and overlying portions of 

 the section may be described in general terms as a series 

 of variable sandstones, clays, and coal beds exposed in low 

 hills and ridges with a dip of 9° or 10° eastward at the base, 

 but decreasing in the upper portions to 5° or 6°, which is 

 about the same as the overlying Wasatch beds. 



The character of the mollusks shows that the lower beds 

 were mostly deposited in brackish waters, but that there 

 were alternations of fresh waters in which the genus Unio 

 thrived with an abundance of individuals . nd great 

 variety of species, and several fresh- water gastropods were 

 common. Between the top of the massive sandstone and 

 the dinosaur horizon there is a band filled with brackish- 

 water fossils, including Ostrea glabra var. arcuatilis Meek, 

 Anomia micronema Meek, Corbula undifera Meek, and 

 Modiola sp. The greater number of the Black Buttes in- 

 vertebrates, however, have been obtained from strata 

 some 40 or 50 feet higher and consequently a little above 

 the dinosaur bed. Here there is a band which in some 

 places is about 4 feet thick, almost wholly made up of 

 shells. By far the most abundant species is Corbicula 

 fracta Meek, and immediately associated with it are Cor- 

 bicula occidentalis Meek and Hayden, Neritina baptista 

 White, N. vahilineata White, and Melania wyomingensis 

 Meek, all of which probably lived in slightly brackish 

 water, for this species of Melania has almost invariably 

 been found associated with brackish-water or marine forms, 

 although it belongs to a fresh-water genus. At the base of 

 this shell bed and immediately above a coal seam Unio 

 shells are abundant. These purely fresh-water forms are 

 found on the slope mingled with the Corbicula shells, but 

 all that were found in situ were either at the base of or a 

 few reet above the Corbicula bed. 



We may now consider the delimitation of the, 

 base of the beds at Black Buttes ( = Laramie 

 of White and many subsequent writers, Black 

 Buttes coal group of Schultz, etc.) in the light 

 of certain recently apquired but hitherto un- 

 published data. Powell described the "Bitter 

 Creek series" as resting with marked uncon- 



formity on the underlying "Point of Rocks 

 series." Meek was inclined to draw the line 

 at the point — if it could be determined — where 

 the fresh-water deposits begin and the es- 

 tuarine or brackish-water deposits cease, "con- 

 sidering the brackish-water deposits most 

 probably Cretaceous, and those above them 

 Tertiary." Bannister described an apparent 

 unconformity beneath 130 feet of "thin sand- 

 stone alternating with grayish shaly clays," 

 which underlie the massive sandstone that 

 forms bluffs 



on the northern edge of the bottom lands of Bitter Creek 

 for a distance of 2 or 3 miles northwest of Black Buttes 

 station, where there appears below them, and apparently 

 dipping unoonformably beneath them, a massive bluish- 

 white soft sandstone. * * * The dip of the underlying 

 beds is nearly southeast about 18°,.'While that of the over- 

 lying rocks is only from 5° to 7° and nearly due east. 



King detected "a slight unconformity be- 

 tween the beds next over the dinosaurian series 

 and the ashy beds which overlie them," which 

 had the effect of placing the AgaihaAimas in the 

 Cretaceous. None of these supposed uncon- 

 formities, however, appear to have been 

 definitely detected and accepted by subsequent 

 students. 



In later years it came to be the prevailing 

 custom to make the massive sandstone so con- 

 spicuous at the base of the exposure the basal 

 portion of the so-called "Laramie" section at 

 Black Buttes, because sedimentation was sup- 

 posed to be uninterrupted between this mas- 

 sive sandstone and the overlying beds, and, 

 moreover, because the sandstone is very 

 sharply delimited from the underlying soft 

 Lewis shale. 



In 1909 A. C. Peale and I spent several weeks 

 in the study of the section at Black Buttes and 

 vicinity. In the massive sandstones a few 

 hundred yards northeast of the station we 

 found numerous specimens of Halymenites 

 major Lesquereux, an alga, which wide expe- 

 rience has shown is present only in marine 

 beds. In addition to this, we found a number 

 of invertebrates which, although fragmentary, 

 were, in the opinion of T. W. Stanton, sufficient 

 to prove that the beds are marine and probably 

 of Fox Hills age. We also observed what we 

 interpreted as an unconformity between this 

 massive sandstone and the overlying soft shales 

 containing the fauna and flora under considera- 

 tion. In the vicinity of the station at Black; 



