INTRODUCTORY REMARKS. 



XXIII 



Section of th< members of the Cretaceous formation on tlie Missouri, and thence westward 



to the Man raises Terres. 



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Clays, sandstones, etc., etc., containing remains of Mammalia. The 

 entire thickness of this formation in the Bad Lands is from. 25 to 250 feet. 



Arenaceous clays passing into argillo-calcareous sandstones 80 feet. 



Plastic clays with calcareous concretions, containing numerous fossils.. 250 feet. 



This is the principal fossiliferous bed of the Cretaceous formation on the 

 Upper Missouri. 



Calcareous marl containing Oslrea congesta, scales of fishes, etc 100 to 150 feet. 



Clay containing a few fossils 80 feet. 



Sandstone and clay 90 feet. 



Buff-colored magnesian limestone of Carboniferous period. 



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This was the first-published section, so far as the writer is informed, show- 

 ing all of the various members and their order of succession, of the marine 

 undoubted Cretaceous series of the Upper Missouri, occupying the space 

 between the well-marked Tertiary above and the Carboniferous below. 

 As may be seen, it embraces the five groups recognized in all of the subse- 

 quently-published sections. Consequently, it may be regarded as the founda- 

 tion, or frame-work, so to speak, of the latter, though the estimated thick- 

 nesses of the beds are now known to be below the maximum as developed at 

 many localities. The great Brackish- and Fresh-water Lignite series, hold- 

 ing a position between the Tertiary beds of the Bad Lands and division 

 No. 5 of this section, was not represented in it, because that formation 

 nowhere occurs along the line traversed by us in 1853 between Fort Pierre 

 and the Bad Lands, though it is well developed farther north. 



In the somewhat numerous papers subsequently published in the joint 

 names of Meek and Hayden, on the rocks and fossils of the Upper Missouri, 

 this section was from time to time amplified by the addition of details, until 

 finally, in our paper of December, 1861 (Proceed. Acad. Nat. Sci. Philad.), 

 it assumed the following complete form, with local geographical names for 

 the first time applied to the subdivisions : 



