9 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 we 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. Meck and Hayden,’ the Cretaceous formations in the region 
of the Upper Missouri, in section, present the following constitution :— 
EARLIER CRETACEOUS— 
No. 1. Yellowish, reddish, and whitish sandstones and clays, with lignite and fossil angiospermous 
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 problematicus, I. tenuirostris, I. fragilis, Ostrea congesta, 
Venilia Mortoni, Phaladomya papyracea, Ammonites Mullani, A. vespertinus, Sca- 
phites Warreni, &e. 
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. pseudo- 
mytiloides, I. aviculoides, Ostrea congesta, &c. p 
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 placenta, A. complexus, Baculites ovatus, B. com- 
and referred to Stenorhynchus vetus (Proc. Acad. Nat. Sci. VI, 377), I also believe to be a Miocene 
fossil. 
Dr. Harlan described the fragment of the femur of a Snipe (Scolopaa), 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. 
1 Dana, Manual of Geology, 1863, 469; Proc. Acad. Nat. Sci. 1861, 419. 
