HISTORICAL REVIEW OF THE LARAMIE PROBLEM. 



65 



Buttes and for many miles southwest of the 

 railroad the uppermost layer of this basal 

 sandstone is a soft white sandstone which can 

 bo easily traced. It has a maximum thickness 

 of 20 feet, but the thickness varies from point 

 to point, in some place being reduced to a foot 

 or less, and in one locality about 2 miles south 

 of the railroad the white sandstone has en- 

 tirely disappeared and the soft shales rest on 

 the yellowish sandstone. At another point 

 about 8 miles southeast of the railroad we 

 observed an irregular trench at least 10 feet 

 deep in this white sandstone, which was filled 

 almost solid with the shells of Corbicula fracta, 

 a well-known species of the upper beds. 



It is but fair to state, however, that the above 

 interpretation of observed conditions has not 

 been accepted by Schultz and other observers, 

 who argue that although the upper white sand- 

 stone may vary in thickness from place to 

 place the variation is due to a lateral change in 

 color from white to brown, and vice versa, rather 

 than to erosion. Peale and I failed to observe 

 an}' locality where there was a lateral change 

 in the color of this sandstone, and the condi- 

 tions as we saw them appeared to indicate a 

 slight unconformity. Moreover, th& inherent 

 probability that this may be correctly inter- 

 preted as an unconformity is indicated by the 

 fact that the massive sandstone marked the 

 close of marine conditions in this region, and 

 further by the fact, as will be shown in a 

 future publication, that the abundant flora 

 gives evidence of being younger than Laramie. 



POINT OF ROCKS. WYOMING, AND VICINITY. 



With the possible exception of Black Buttes, 

 no locality in this region has given rise to more 

 extended discussion than Point of Rocks. 

 The section is well exposed in the bluff just 

 north of the station and consists of massive 

 white sandstones and soft clay shales and coal 

 beds. The plants have been found mainly in 

 proximity to the coal. These beds constituted 

 the '"Point of Rocks series" of Powell and were 

 described by him as strongly unconformable 

 beneath the "Bitter Creek series." Powell, 

 Meek, and White agreed in regarding these 

 beds as of Cretaceous age, but Lesquereux from 

 his studies of the plants considered them as 

 Tertiary. After the Laramie formation was 

 established the beds at Point of Rocks were 



referred by White and others to this formation, 

 or group, as it was then called, and this disposi- 

 tion remained undisputed for many years. 



In 1897 Stanton and I '* pointed out that the 

 coal and plant bearing beds at Point of Rocks 

 are below marine Cretaceous beds containing a 

 Fox Hills fauna and hence could not be of 

 Laramie age. The statement was as follows: 



At Point of Rocks, 11 miles northwest of Black Buttes, 

 a lower series of coal-bearing beds is well exposed in cliffs 

 and high hills nortli and east of the station. Here, as at 

 Black Buttes, the base of the e.xposure is formed by a 

 massive light-colored sandstone about 100 feet thick, and 

 this fact, together with evidence of local faulting along 

 the railroad between the two places, has led several 

 geologists to regard the two exposures as representing about 

 the same horizon. Our observations confirm those of 

 Meek and Bannister in putting the Point of Rocks coal 

 beds several hundred feet lower than those at Black Buttes, 

 and we discovered the additional fact that a considerable 

 portion of the intervening strata consists of marine beds 

 and contains a Fox Hills fauna. The uneven upper sur- 

 face of heavy sandstone at Point of Rocks was regarded by 

 Powell as evidence of an erosion interval which separated 

 the Point of Rocks group below from the Bitter Creek 

 group above. The larger number of fossil plants described 

 from this locality were obtained in argillaceous lenticular 

 masses in the upper part of the sandstone. Others are 

 associated with the coal beds, of which there are several in 

 the series of soft sandstones, sandy shales, and clays ex- 

 posed in the bluffs north of Point of Rocks station to a 

 thickness of about 260 feet above the massive sandstone. 

 Above the middle of the coal-bearing part of the section 

 two fossiliferous bands have yielded a fe.w species of inver- 

 tebrates, consisting of one marine shell, four brackish-water 

 forms, and one fresh-water form. * * * 



In the neighborhood of Point of Rocks the dip of the 

 beds is about 6= a little north of east, almost parallel vrith 

 a valley that joins that of Bitter Creek just east of the 

 station, so that the heavy sandstone soon disappears 

 beneath the surface and the beds above it successively 

 come down to the valley level in the hills on its north 

 side. * * * The beds on the top of the bluffs north of 

 the station thus come down to the valley a little over a 

 mile east of that place, and immediately above them, in a 

 brown ferruginous sandstone, marine Cretaceous species 

 indicating a Fox Hills horizon were found. » * * 



Above this horizon there are few exposures seen on 

 going eastward until a line of cliffs is reached nearly 4 

 miles east of Point of Rocks. These cliffs show at their 

 base about 150 feet of clay shales with bands of sandstone, 

 and a concretion in the clay yielded BacuHtes ovatus Say, 

 Lunatia occidentalis Meek and Hayden, and Maclra sp., 

 showing that this horizon, some 700 feet above the last 

 one mentioned, is still in the Fox Hills. The shales are 

 overlain by massive sandstone somewhat over 100 feet 

 thick, yellowish brown below and nearly white abo^-e, and 

 this is succeeded by a series of shales, sandstones, and coal 



M Stanton, T. W., and Knowlton, F. H., Stratigraphy and paleontol- 

 ogy of the Laramie and related formations in Wyoming: Geol. Soc. 

 America Bull., vol. 8, p. 146, 1S97. 



