64 



SCIENCE 



[S. S. Vol. XXXII. No. 810 



the Fox Hills sandstone which was long ago 

 described in this area by Meek and Hayden, who 

 named it from its typical occurrence in the Fox 

 Hills, which form a ridge between the Cheyenne 

 and Moreau rivers and extend to the Missouri 

 north of the Moreau. It is a shallow-water or 

 littoral deposit of variable character usually not 

 much over 100 feet thick in this area. It yields 

 an abundant invertebrate fauna closely allied to 

 that of the underlying Pierre, but with some 

 distinctive species. 



Above the Fox Hills sandstone there is a non- 

 marine formation several hundred feet thick which 

 is correlated with the so-called " Ceratops beds " 

 of Wyoming, as it contains abundant remains of 

 the dinosaur genera Triceratops and Trachodon 

 and other reptiles belonging to the same fauna. 

 It also yields fossil plants which have been iden- 

 tified as belonging to the flora of the " Lower Fort 

 Union," to which horizon the " Ceratops beds " 

 of other areas have also been assigned on the 

 evidence of fossil plants. The Fort Union forma- 

 tion is supposed to be later than the Denver. 

 Hence, if the " Ceratops beds " are Fort Union, 

 where they rest on the Fox Hills there is a break 

 in the sedimentary record which represents the 

 Laramie, Arapahoe and Denver formations. In 

 the examination of the area last summer by 

 Geological Survey parties a somewhat eroded and 

 channeled surface in the upper part of the Fox 

 Hills sandstone was found at many points and 

 was at first interpreted as an important uncon- 

 formity giving evidence of the break above men- 

 tioned. The uneven surface is a,t the base of 

 brackish-water bed full of shells of Ostrea, 

 Anomia, Corhicula, etc., belonging to the same 

 types and usually specifically identical with forms 

 that occur in the Laramie. In the same bed with 

 the brackish-water shells, and associated in such 

 a way that they must have lived contemporane- 

 ously, a number of typical marine species belong- 

 ing to the Fox Hills fauna were found. These 

 include Scaphites conradi (Morton), Scaphites 

 conradi var. intermedius Meek, Scaphites cheyen- 

 nensis (Owen), Lunatia suborassa M. & H., 

 Teredo sp. and Tancredia americana M. & H. 



This commingling of the marine Fox Hills spe- 

 cies with the brackish-water fauna above the 

 eroded surface was found at five localities dis- 

 tributed over an area about forty miles square. 

 It proves that the erosion was geologically con- 

 temporaneous with the sedimentation and that the 

 brackish-water bed really belongs to the Fox Hills. 



The wide-spread occurrence of this brackish-water 

 bed at the top of the marine deposits and the 

 absence of evidence of an unconformity immedi- 

 ately above it give strong evidence that there was 

 a gradual transition from marine to land and 

 fresh-water conditions. 



In the southwest part of North Dakota on the 

 Little Missouri, where there is a similar develop- 

 ment of Fox Hills sandstone, the change from 

 marine to land conditions is locally abrupt, so 

 that lignitic land deposits rest directly on an 

 uneven surface of the sandstone, but about 500 

 feet higher in the section there is an oyster bed 

 with Cretaceous species of Ostrea indicating that 

 the sea had not left the region until after a large 

 part of the " Ceratops beds " was deposited. 



In the Lance Creek area of Converse County, 

 eastern Wyoming, the Fox Hills sandstone devel- 

 ops a thickness of about 500 feet and in its upper 

 part contains thin coal beds and other evidences 

 of land conditions intercalated in marine strata. 

 At the top there is a brackish-water zone followed 

 by the " Ceratops beds." The evidence is in 

 favor of a gradual transition and practically con- 

 tinuous sedimentation rather than a long unrepre- 

 sented interval. 



The three areas discussed tell a story of gradu- 

 ally changing conditions near the end of the Cre- 

 taceous when the uplift of the Rocky Mountain re- 

 gion was draining the interior sea. The uplift was 

 neither uniform nor continuous and the emergence 

 above sea level could not have been simultaneous 

 for all localities throughout the region. As the 

 sea became shallow the effect of tidal currents and 

 wave action was shown in irregular deposition, 

 cross-bedding and local erosion, and when an area 

 was elevated above tide the deposits formed were 

 subjected to all the varying conditions of flood 

 plains, deltas and marshes. It would depend on 

 the configuration of the coast, the topography and 

 drainage of the adjacent land and the rate of 

 elevation whether at any particular locality the 

 last marine bed would be covered by a brackish- 

 water deposit or followed immediately by land 

 conditions. 



The bearing which the facts here presented have 

 on the Laramie problem is self-evident. If there 

 is a transition with practically continuous sedi- 

 mentation from the Fox Hills sandstone into the 

 •■ Ceratops beds " in the region discussed, then 

 these "Ceratops beds" include the Laramie. 



Feancois E. Matthes, 



Se(fretary 



