LoGaN. | The Upper Cretaceous. 215 
a never failing spring of water is found at the eastern extremity of 
the sandstone and shale conjunction. 
The sand grains of the Dakota sandstone are rarely so closely 
cemented together as not to permit the free circulation of water. A 
few mounds of shale in Elsworth county, however, are surmounted 
by a layer of sandstone the grains of which cohere so closely that 
the water is shed and very little, if any, stored. 
THE BENTON. 
The dividing line between the Dakota and Benton is marked 
lithologically by the change from sandstone to shale, or from bitu- 
menous to argillaceous shale. 
GEOGRAPHY. 
In geographical extent the Benton is the largest of the Cretaceous 
groups. It extends from the north line of the state in Republic 
county to Ford county on the southwest. With the exception of 
two small outcrops, one in Hamilton and one in Gray county, the 
Benton area lies north of the Arkansas river. It seems to be con- 
formable with the Upper Dakota, and the dip of its strata is toward 
the northeast. 
STRATIGRAPHY. 
Lithologically the Benton! may be divided into two groups, viz., 
the lower, or limestone group,’ and the upper or shale group.2 The 
iower group includes all the limestone and the interbedded and un- 
derlying shale. The upper group includes all the shales above the 
limestone group and below the Fort Hays limestone of the Niobrara. 
THE LOWER GROUP. 
The lower group contains five principal horizons, namely: 
1, Bituminous shale; 2, Lincoln Marble;* 3, Flagstone; 4, Ino- 
ceramus; 5, Mence-post. The entire thickness of this group is from 
1 For reasons that will be evident from the discussion of the Benton, the nomen- 
clature of that group employed by Prof. I’. W. Cragin in his paper, ‘‘On the Stratig- 
raphy of the Platte Series,’ has been somewhat changed. ! 
2 Russell Formation—Cragin. 
3 Victoria clays—Cragin. 
4 On stratigraphy of Platte series—Cragin. 
