MEEK AND HAYDEN'S CRETACEOUS SECTION. 171 



SECTION OV THE ]vnOMRKI{S OF THE CKETACKOIS I'OKMATION, AS OKSKIJVICD ON 

 TUE MISSOUUI ItlVEU AND THENCE WESTW AIJU TO THE MAUVAISES TEKUES. 



Tert ia nj Jo r m a t io h . 



Clays, sandstoiies, etc., coiitniiiiiif,' rt'iuains of MaiumaJia. The eutire tliiekiiess 

 of this foiTuatiou iu the bad lands is from 2') to 250 feet. 



Cretaceous Formation. 



Feet. 



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



4. iMasti(^ <*li>,V, with calcareous coucretious, contaiuinji- nuuu'rous fossils. This 

 is the priucipallossiliferous bed of the Cretaceous formation upon theuj)])er 



Missouri 250-.'}50 



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



2. Clay, coutaiuing a few fossils 80 



1. Sandstone and clay 1)0 



Subsequently tlie country was visited by Dr. Hay den 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 nmcli new material was published by ]\Ieek and Hayden 

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

 above section, until in their joint paper of December, 18G1 (Proc. Acad. 

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

 presented, with the geograi)hical names which remain now the accei)ted 

 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, Haiitihis Delayi, Placenticeras placenta^ P. lenticularis, Sca2)hiies 

 Conradi, 8. NicoUeti, BavnWes ffrandis, Pijropsis Bairdi^ Piestochilus Culbertsoni, Pi/ri- 

 fusus Xewherryi, Aucluira Americana, Pscudohiiccinum Xcbrasecnse, Mactra Warrcnana, 

 Cardium subqnadratiim, and a great number of other moUuscau fossils, together with 

 the bones of Mosasanrus Missourieytsis, etc. 



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

 along the base of the Big Horn Mountains, and on Xorth and South Platte Eivers. 



Thickness, 500 feet. 



