408 WEED AND PIRSSON 
Spirifer centronata Winch. ‘The general expression of these 
fossils is Lower Carboniferous.” 
Jurassic.—Overlying the massive, structureless limestones 
which form the top of the Carboniferous series and are really 
the most prominent sedimentary rocks of the region, are thinly 
bedded rocks which generally form somewhat gentle slopes at 
the base of the steep limestone cliffs, or bedding slopes. These 
rocks form somewhat detached hillocks of the hogback style, 
the hillocks being fifty feet high and separated from the lime- 
stone slopes by a gentle sag or depression. These beds consist 
of shaly, gray limestones, carrying Jurassic fossils and changing 
gradually into impure, marly shales and argillaceous limestones, 
carrying a fauna of marked Jurassic types. The total thickness 
is about 100 feet. Good exposures of these beds are found near 
the town of Landusky, where the road descends from the heights 
along the slope of Indian Butte. The following fossils collected 
from these beds have been examined by Mr. T. W. Stanton, who 
reports the presence of the following species: 
Ammonites; fragments of an undecided species. 
Belemnites densus M. and H. 
Pleuromya subcompressa Meek. 
Astarte Meeki Stanton (ms). 
Modiola subimbricata Meek. 
Gryphea calceola, var. nebrascensis M. and H. 
“This is evidently from the Jurassic horizon that is so well rep- 
resented in the Yellowstone Park and adjacent parts of Montana.”’ 
Cretaceous.—TVhe Jurassic rocks are capped by a bed of buff- 
colored, massive sandstone which weathers red and is six feet in 
thickness, the rock merging into a variety that breaks down so 
readily, forming a sandy soil, that no outcrops are seen; its 
thickness is about twenty feet. This sandstone is capped in turn 
by a thickness of gray, arenaceous shales. These last beds are 
in turn capped by sandy shales for at least’ 300 feet, above 
which there is a sandstone bed of five to ten feet in thickness, 
which when exposed forms a long wooded ridge separating the 
depressions eroded in the soft shales. This sandstone lies at 
