MEEK AND HAYDEN'S CRETACEOUS SECTION. 171 



SECTION OF THE MEMBERS OF THE CRETACEOUS FORMATION, AS OBSERVED ON 

 THE MISSOURI RIVER AND THENCE WESTWARD TO THE MAUVAISES TERRES. 



Tertiary formation. 



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

 of this formation in the bad lands is from 25 to 250 feet. 



Cretaceous Formation. 



Feet. 



5. Arenaceous clay, passing into argillo-caleareous sandstones 80 



4. Plastic clay, with calcareous concretions, containing numerous fossils. This 

 is the principal fossiliferous bed of the Cretaceous formation upon the upper 



Missouri 250-350 



3. Calcareous marl, containing Ostrea congesta, scales of fishes, etc 100-150 



2. Clay, containing a few fossils 80 



1. Sandstone and clay .... 90 



Subsequently the country was visited by Dr. Hayden alone and after- 

 wards in connection with the reconnaissances of Lieutenant Warren and 

 Captain Raynolds. From these various explorations the Cretaceous became 

 better known, and much new material was published by Meek and Hayden 

 at various times, including descriptions of new fossils and revisions of the 

 above section, until in their joint paper of December, 1861 (Proc. Acad. 

 Nat. Sci. Phila.) their final subdivision of the Cretaceous in the West was 

 presented, with the geographical names which remain now the accepted 

 nomenclature of the formation in the Northwest. 



The following is their section of the Cretaceous of the upper Missouri 



country, as given in Professor Meek's Invertebrate Paleontology of the 



United States Geological Survey of the Territories, with the addition of a 



short synopsis of the character and estimated thickness of the different 



groups as they were found around the Black Hills; the divisions are given 



in descending order. 



No. 5. — Fox Hills group. 



Gray, ferruginous, and yellowish sandstone and arenaceous clays, containing 

 Belemnitella bulbosa, Nautilus Delmyi, Placenticeras placenta, P. lenticularis, Scapliites 

 Conradi, S. Nicolleti, Bavuliles grandis, Pyropsis Bairdi, Piestochilus Culbertsoni, Pyri- 

 fusus Wewberryi, Auchura Americana, Pseudobuccinum Nebrascense, Mactra Warrenana, 

 Cardium subquadratum, and a great number of other molluscan fossils, together with 

 the bones of Mosasaurus Missouriensis, etc. 



Localities. — Fox Hills, near Moreau River ; near Long Lake, above Fort Pierre ; 

 along the base of the Big Horn Mountains, and on North and South Platte Rivers. 



Thickness, 500 feet. 



