HISTORICAL REVIEW OF THE LARAMIE PROBLEM. 



63 



did not succeed in finding any trace of verte- 

 brate remains, though the horizon that had 

 afforded the celebrated Agalhaumas was at 

 least approximately placed and tlie beds care- 

 fully searched. The conclusion was reached 

 that the beds here under consideration rest 

 conformably on the underlying Cretaceous and 

 pass upward wathout observed discordance 

 into beds then identified as Fort Union and 

 Wasatch. They seemed to fill all the require- 

 ments demanded by the definition of the Lara- 

 mie and were so referred. 



For a number of years after the publication 

 of the above-mentioned paper there was little 

 activity in the study of the Black Buttes 

 region. In 1907 A. R. Schultz - and party 

 made an investigation of the coal resources of 

 the northern part of the Rock Springs coal 

 field and reached important conclusions con- 

 cerning the geology of this and adjacent areas. 

 The oldest rocks exposed in the region were 

 identified as of Montana age, and names were 

 applied to them that had been established in 

 southern Colorado. The lowest, called the 

 Mesaverde formation, is made up of four mem- 

 bers and aggregates 5,000 feet in thickness. 

 Conformably above the Mesaverde is the Lewis 

 shale, composed of soft gray, drab, and black 

 gypsiferous shale and soft shaly sandstones 

 and forming a region of low relief. The lower 

 part of the Mesaverde was said to include in 

 the main the "Point of Rocks series" of 

 Powell, and the upper part of the Mesaverde 

 and the Lewis shale Schultz assigned to the 

 "Bitter Creek." Above the Lewis shale and 

 apparently conformable with it is the so-called 

 Black Buttes coal group, which was described 

 by Schultz, as follows: 



Along the east side of the [Rock Springs] dome the 

 Black Buttes coal group lies conformably upon marine 

 Lewis shale, which weathers readily and produces regions 

 of low relief. The basal member of the Black Buttes 

 coal group consists of a massive bed of yellowish-white 

 sandstone, in places over 100 feet thick and not known to 

 be coal bearing. This member, resting upon the soft, 

 friable Lewis shale, forms steep hills and cliffs along the 

 contact. The rocks above the sandstone consist of a series 

 of variable sandstones, clay, and coal beds that lie ex- 

 posed in the low hills and ridges east of the main scarp. 

 On the west side of the dome this group is absent. 



In the tabular statement the Black Buttes 

 coal group was referred to as Laramie ( (). Its 

 maximum thickness in. tliis field was given as 



» U. S. Geol. Survey Bull, 341, pp. 2.56-282, 1909. 



2,371 feet. Resting unconformably on the 

 Black Buttes coal group is the Black Rock 

 coal group, which in the table was classed as 

 Wasatch, although in the discussion Schultz 

 stated that it " is thought to belong to the Fort 

 Union formation." In thickness it ranges from 

 1,200 to over 2,600 feet. The Black Rock coal 

 group was briefly described by Schultz as 

 follows : 



At the base is a thin band of conglomerate, ranging in 

 thickness from 2 to 6 feet. The pebbles are very fine, 

 consisting mostly of quartz, although in many places other 

 pebbles are present. This conglomerate marks an uncom- 

 formable contact between this coal group and the Black 

 Buttes. Lithologically this group resembles the upper 

 part of the Black Buttes coal group. The sandstone and 

 shale, however, are more highly colored and more poorly 

 cemented and contain a large number of spherical and 

 irregular concretions. The formation is prolifically coal 

 bearing. 



In the following season (1908) Schultz -^ in- 

 vestigated the southern part of the Rock Springs 

 coal field, which included the Black Buttes 

 area, though Black Buttes is really on the line 

 between the two areas. The section up to and 

 including the Black Buttes coal group was 

 found to be the same as that just described for 

 the northern part of the Rock Springs dome, 

 but above this point in the general section of 

 the whole region a number of differences were 

 discovered. Although not then known to be 

 anywhere exposed in the Rock Springs dome, it 

 appeared from studies in the Rawlins area, to 

 the east, that there is an immense series of soft 

 sandstones and shales, called the Knobs- 

 Cherokee coal group, with a thickness of 6,000 

 to 9,400 feet, which is to be intercalated be- 

 tween the Black Buttes and Black Rock coal 

 groups. If these thicknesses are even approxi- 

 mately correct, as they are believed to be, the 

 unconformity between these two series of beds 

 is of course one of tremendous magnitude. As 

 regards the age determinations, the Knobs- 

 Cherokee coal group was referred by Schultz to 

 the ''Upper Laramie" of Veatch as defined in 

 Carbon County, Wyo., while the Black Rock 

 coal group was still referred to the Wasatch, 

 although containing a Fort Union flora. 



The general geologic relations of the Black 

 Buttes area having been discussed, a more de- 

 tailed description of the beds in question may 

 now be given. The following is quoted from 



MU. S. Geol. Survey Bull. 3S1, p. 214, 1910. 



