GEOLOGY OF THE LARAMIE PLAINS 



feet thick. Along the margin of the mountains east of the 

 Wasatch it is generally present. Hayden says that it is doubtful 

 if any geologist would ever make three divisions of Nos. 2, 

 3 and 4 if he had first studied them in the mountains. Hence 

 the name "Colorado" used to include them seems appropriate. 



After passing Cooper Station, five miles due east, black 

 clays of the Lov^er Cretaceous appear and six miles south- 

 east of Como on the railroad are excellent sandstone quarries, 

 and numerous vegetable impressions occur. 



Clarence King, in his 40th Parallel Report, gives a gen- 

 eralized section of Cretaceous east of the Colorado range, 

 from the base up. 



Number II. Fort Benton. I st — Dark plastic ferruginous and 

 argillaceous clays. 



2d. Grayish blue clays, becoming dark calcareous near the 

 top, 200 to 500 feet. 



No. III. Niobrara. I st — Argillaceous limestone, some- 

 times merging into the dark Benton shales. 



2d — Light variegated marls; yellow^ color prevails. 



3d — ^ Yellow, white and cream colored marls with gypsum. 



4th — Whitish gray marls. 



5th— Yellow marls, with intercalated limestone. 



6th — Bluish gray, soft, earthy beds, calcareous and argilla- 

 ceous of variable thickness, 100 to 200 feet. 



No. IV. Fort Pierre. 1st— Black, carbonaceous, shales 

 and marls. 



2d — Marly black arenaceous shales. 



3d — Interstratified clay and sand, 250 to 300 feet. 



Total, Colorado, 600 to 1 ,000 feet. 



King, in 40th Parallel Survey, says that the Fort Benton 

 Cretaceous occurs as dark plastic clays and thin shales. The 



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