Mesozoic and Ccenozoic Geology and P alee ontology. 19 



In 1854,* the Cretaceous formation of Nebraska was subdivided b}' 

 Hall and ]Meek. in ascending order, as follows: 



1. Sandstone and chn', 90 feet. 



2. Cla}^ containing a few fossils, 80 feet. 



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

 100 to 150 feet. 



4. Plastic claj's, with calcareous concretions, containing numerous 

 fossils, 250 feet. This is the principal fossiliferous bed of the Cre- 

 taceous formation on the Upper Missouri. 



5. Arenaceous clays passing into argillo calcareous sandstones, 80 

 feet. 



These subdivisions were referred to, by these numbers, until 1861, 

 when Meek and Hayden, in accordance with the laws of nomenclature, 

 gave them the following geographical names: No. 1, Dakota Group; 

 No. 2, Fort Benton Group; No. 3, Niobrara Group; No. 4, Fort Pierre 

 Group; and No. 5, Fox Hills Group. 



They described from No. 5, at Fox Hills, Pecten rigida, now Syn- 

 cyclonema rigiduin, from the Bad Lands of Dakota, BacuUtes grandis; 

 from No. 4, at the Great Bend of the Missouri, below Fort Pierre, 

 Avicula haydem', Inoceramns convexus, I. tenuilineatus, I. subloivis^ 

 Nucula subnasuta, now Nuculana subnasuta, Buccinum vinculum, 

 now Trachijtriton vinculum. Ammonites complexus, Turrilites 

 cochleac'us, now Heteroceras cochleatum: from Sage creek, JSfucula 

 ventricosa, now Toldia ventricosa, Crassatella evansi, Lucina subun- 

 data, Dentalium gracile, Actoion concinnus, now Cinulia concinna, 

 Fusus tenuilineatus, now Closteriscus tenuilineatus, Natica concinna, 

 now Lunatia concinna, Natica paludiniformis, now Amauropsis, 

 IKiludiniformis, Fusus constr ictus, now Odontobasis cojistricta; from 

 No. 2, near the mouth of Vermilion river, Inocer amus fragilis-, ivom 

 below the mouth of James river, Cytherea orbiculata, now Callista 

 orbiculata and C. tenuis; from No. 1, at the mouth of Big Sioux river, on 

 the Missouri, Pectunculus siouxensis, now Trig'onarca siouxensis. 



Dr. Geo. G. Shumardf found the Cretaceous rocks at Fort Washita, 

 and extending from, there uninterruptedly to the southwestern boun- 

 dary of the Cross Timbers, in Texas. It usually consists of grayish 

 yellow sandstone, with intercalations of blue, yellow and ash colored 

 clays, and beds of white and bluish white limestone. The limestone 

 reposes on the clays and sandstones, and in some places attains a 



=•= Mem. Am. Acad. Arts & Sci., vol 5. 



t Expl. of Red River, of Louisiana, by Marcy. 



