2 INTRODUCTION. 



Most of the fossil remains which form the subject of the memoir were obtained 

 in New Jersey, and are contained in the museum of the Academy of Natural 

 Sciences of Philadelphia. Very many of them were found in the Green-sand, 

 which, under the name of Marl, is largely excavated for agricultural purposes; 

 others were obtained from limestone. Many specimens have been derived from 

 Maryland, Delaware, North Carolina, Georgia, Alabama, Mississippi, and Nebraska. 



The Cretaceous formations compose a large tract extending through the States 

 of New Jersey, Maryland, and Delaware. They also appear in isolated patches 

 in North and South Carolina, and Georgia. More extensively developed in the 

 western portion of the latter State, they curve in a wide crescentoid tract through 

 Alabama, Mississippi, and Tennessee to the mouth of the Ohio River. Thence 

 passing in a narrow band through Arkansas, they afterwards expand to an enormous 

 extent and occupy a great portion of the region between the Mississippi River 

 and the Rocky Mountains, reaching north into the British possessions, and south 

 into Mexico. 



When Ave consider the great development of the Cretaceous formations in the 

 western and southern portions of the United States in comparison with those on the 

 eastern border, from which nearly all our fossils have been obtained, we may antici- 

 pate many additions. These will not only increase the number of species and 

 genera, but will serve to clear up many of the obscurities concerning those already 

 in our possession. 



According to Messrs. Meek and Hayden,^ the Cretaceous formations in the region 

 of the Upper Missouri, in section, present the following constitution : — 



Earliee Ceetaceous — 

 No. 1. Yellowish, reddish, and whitish sandstones and clays, with lignite and fossil angiospcrmous 



leaves, 400 feet in thickness. Located near Dakota, and reaching southward into 



northeastern Kansas. 

 No. 2. Gray laminated clays, with some limestone, 800 feet in thickness. Located near Fort 



Benton, on the Upper Missouri, also below the Great Bend. Characteristic fossils of 



this division are Inoceramus prublematicus, I. tenuirostris, I. fragilis, Osirea congesta, 



Venilia llortoni, Pholadomya jMjnjracea, Ammonites 3Iullani, A. vespertinus, Sca- 



phites Warreni, &c. 

 No. 3. Grayish calcareous marl, 200 feet in thickness. Location : Bluffs on the Missouri, below 



the Great Bend. Characteristic fossils consist of Inoceramus problematicus, I. pjseudo- 



mytiloides, I. aviculoides, Ostrea congesta, &c. 



Later Cretaceous — 



No. 4. Plastic clays, 700 feet in thickness : the middle portion barren of fossils. Located on the 



Missouri near Great Bend, about Fort Pierre, extending to the Bad Lands, on Sage 



Creek, Cheyenne River, and White River above the Bad Lands. Characteristic fossils 



are Nautilus Dekayi, Ammonites pjlacenta, A. complexus, Baculites ovatus, B. com- 



and referred to Slenorhynchus vetus (Proc. Acad. Nat. Sci. VI, STY), I also believe to be a Miocene 

 fossil. 



Dr. Harlan described the fragment of the femur of a Snipe (Scolojmx), from the Marl of New 

 Jersey (Med. and Phys. Res., 282), which has been accepted by authors as an ornithic fossil of the 

 Cretaceous period. The specimen, preserved in the museum of the Academy, is of recent origin. 



» Dana, Manual of Geology, 18G3, 4C9; Proc. Acad. Nat. Sci. 1861, 419. 



