174 T. ir. Stanton — Fox Hills Sandstone. 



fine clays of the latter to the more sandy material above being 

 usually very gradual. Nor are these two formations distin- 

 guished by any abrupt change in the organic remains, since 

 several of the fossils occurring in the upper beds of the Fort 

 Pierre group pass up into the Fox Hills beds, while at some 

 localities we find a complete mingling in the same bed of the 

 forms usually found at these two horizons." The total thick- 

 ness of the formation was then estimated at 500 feet, but in 

 previous papers dealing with only the typical area the thick- 

 ness was given as 100 to 150 feet, an estimate which is nearer 

 the truth for this particular area. 



The variable character of the formation is indicated by 

 Meek and Hayden's description just quoted and this vari- 

 ability as to details becomes impressive after a number of lopal 

 sections have been examined. In some exposures nearly the 

 whole formation is a soft, friable, cross- bedded gray or yellow- 

 ish sandstone, usually with many iron-stained concretions and 

 indurated masses as on Cannonball River, 6 miles above its 

 mouth, where single exposures show 60 feet of sandstone and 

 the base of the formation is not seen. At other places similar 

 sandstones occur at the top and at the bottom and include 

 indurated beds of considerable extent, while the middle portion 

 of the formation is made up of more or less sandy shale in 

 bands a few inclies thick of alternating lighter and darker color. 

 This banded shale contains considerable vegetable matter in the 

 form pf stems and comminuted fragments and in general 

 lithologic character it closely resembles some parts of the over- 

 lying Lance formation. At still other localities within short 

 distances either the upper sandstone or the lower one or some- 

 times both of them are found to thin or disappear as distinct 

 beds, their places being taken by more shaly material. The 

 whole formation gives ample evidence of irregular sedimenta- 

 tion in the presence of strong, variable currents. 



The irregular character of the formation may be shown by 

 describing a few local sections beginning on Grand River near 

 the mouth of Dirt Lodge Creek about 20 miles southwest of 

 McLitosh, South Dakota. On the south side of the river the 

 following section is exposed : 



Section on Grand River near the mouth of Dirt Lodge Creek. 



Feet 



1, Hard gray sandstone with Tancredia americana and 



Halymenites - .- 15 



2. Banded shale with Fasciolaria scarboroughi, Thracia, 



Anchura, Scaphites, etc 50 



:i. Hard gray sandstone with Tancredia americana and 



Halymenites — 10 



4. Soft yellowish massive sandstone 40 



5. Dark clay shale referred to the Pierre, exposed 75 



