CRETACEOUS (krA-ta'slyCis) SYSTEM, or CHALK FORMATION (Lat. cretacens, chalky, from ereta, chalk). A term applied to a series of strata underlying the Tertiary and resting on the Jura Trias, the name being derived from the chalk beds which form such a prominent member of the Cretaceous in England and France. although such ebalk-beds are rare in the United States. occur ring only in Texas and Arkansas. There exists at times an unconformity between the Upper Cre taceous and the Eocene, or lower member of the Tertiary, especially in the United States. The classification of the Cretaceous presents many difficulties. owing to the variable section which it exhibits in different areas; but European and American geologists arc agreed on a division into an upper and a lower member, while for divisions of lesser size local names are employed.
The Lower Cretaceous is represented in the northern Gulf States by (a) Tuscaloosa and (b) Eutaw stages; in Texas and the western Gulf borders by (a) Trinity, (b) Fredericksburg, and (c) Washita stages. The Upper Cretaceous in the Rocky Mountain region has the following subdivisions: (a) Dakota stage, (b) Benton stage, (e) Niobrara stage, (d) Pierre stage. (e) Fox Hills stage, (f) Laramie stage; while in the Atlantic border States it is divided into (a) Raritan stage and (b) New Jersey Greensand stage. The Cretaceous rocks of North America form a belt of increasing width, extending south ward along the Atlantic coast from New York, New Jersey, Maryland, North Carolina, Georgia, and Florida; then around the northern and western shores of the Mexican Gulf, up the Mississippi Valley to the mouth of the Ohio, and from Texas northward to the foothills of the Rocky _Mountains. They occur also in Nebraska, Kansas, and Iowa. The greatest development of the Cretaceous system is in Wyoming, Utah. Colorado, and west of the Sier ra Nevadas in California. In some portions of these last-named regions it is found at heights of 10.000 and 12.000 feet. It occurs also in Arctic America, near the mouth of the Maekenzie River. The American Cretaceous beds consist of greensand—called also 'marl,' and much used in New Jersey and elsewhere for fertilizing land —sands of other kinds, clays, shell deposits, and, on the Gulf of Mexico, especially in Texas, lime stone. In New Jersey the formation is 400 or
500 feet thick; in Alabama, 2000 feet; in Texas, S00 feet, chiefly solid limestone; in the upper Missouri basin more than 2000 feet; and east of the Wasatch, more than 9000 feet.
The rocks of the Cretaceous contain an abun dance of both animal and plant remains, for this was a closing period of an era in which reptiles predominated, and, curiously enough, but few or none of the Cretaceous species have continued into the Tertiary. The plants found in the Cre taceous represent angiosperms, which were not found before this era, both dicotyledons and palms, the former including species of the oak, willow, poplar, beech, maple. fig, tulip, sassafras, eucalyptus. and sequoia. Many palms and cyeads are found in the Cretaceous of North America. The appearance of the dicotyledons in this for mation is rather sudden. The animal remains found include both the smallest and largest forms. There are foraminifera, sponges (which were very common in the chalk). echinoids, many mollusks, especially spirally coiled ammonites, and oysters. The fishes show a continuation of the placoids and ganoids of the former era; but teleosts, or time bony fishes, made their first-ap pearance. There was also an extraordinary abundance of reptiles, including enaliosaurs, dinosaurs. pterosaurs, and crocodiles. Some of the pterosaurs from the Kansas rock meas ured from 20 to 25 feet in expanse of wing. The sea-saurians were from 10 to 50 feet long. Cope describes the elasmosaurus as a snake-like form 40 feet long, with an arrow shaped head on a swan-like neck that rose 20 feet out of the water. Consequently it could swim many feet below the surface, and yet have its head extended into the air for breath. The American rocks supply 40 species of sea serpents. More curious still were the birds with teeth, found in New Jersey and Kansas. (See