Mesozoic and C'ccnozoic Geology and Paleontology. 55 



In 1854,* the Cretaceous formation of Nebraska was subdivided by 

 Hall and Meek, in ascending order, as follows: 



1. Sandstone and chw, 90 feet. 



2. Clay 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 fossil iferous bed of the Cre- 

 taceous formation on the Upper Missouri. 



5. Arenaceous cla3^s passing into argillo calcareous sandstones, 80 

 feet. 



These subdivisions were referred to, by these numbers, until 18fil, 

 when Meek and Haj'den, in accordance with the laws of nomenclature, 

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

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

 Group; and No. 5, Fox Hills Group. 



The3^ described from No. 5, at Fox Hills, Pecten rigida, now Syn- 

 cycloneina rigidum, from the Bad Lands of Dakota, Baculites grandis\ 

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

 Avicula haydeni, Inoceramus convexus, I. tenuillneatus^ I. sublaivis., 

 yucula subnasuta, now JSTuculana subnasuia, Buccinum vinculum., 

 now Trachytriton vinculum, Ammonites complexus, Turrilites 

 cochleaius, now Heteroceras cochleatum; from Sage creek, N'ucula 

 venti'icosa, now Yoldia veniricqsa., Crassatella evansi, Lucina subun- 

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

 Fksks tenailineatus. now Closterisciis tenuilineatus, Natica concinna, 

 now Lunatia concinna, Natica paludiniformis, now Amauropsis, 

 pahidiniformis, Fusus consirictus, now Odontobasis constricta' from 

 No. 2, near the mouth of Vermilion river, Inoceramus fragilis; from 

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

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

 the Missouri, Pectunculus siouxensis, now Trigonarca 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 cla3's and sandstones, and in some places attains a 



* Mem. Am. Acad. Arts & Sci., vol 5. 



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



