CRETACEOUS SYSTEM, the highest division of the Mesozoic or Secondary strata, rests conformably upon the JURASSIC SYSTEM, and is overlaid uncon formably by the oldest deposits of the EocENE SYSTEM. The Cretaceous strata of Great Britain are confined chiefly to the E. and S. E. of England. They form the Yorkshire Wolds, extend over large parts of Norfolk, Suffolk, and Hertford, and compose the Chiltern Hills, Salis bury Plain, the Downs, and the S. part of the Isle of Wight. On the Continent the Cretaceous rocks form a broad basin in the N. of France, and stretch E. from Belgium, Holland, Denmark, and the S. of Sweden, through the great plains of northern Europe to the S. end of the Ural Mountains; but over extensive re gions within that wide area they lie more or less concealed under younger forma tions. There is another extensive de velopment of Cretaceous strata in south ern Europe, where they enter largely into the composition of many of the Mediterranean coast-lands. The chief petrological feature of the Cretaceous strata of western and northern Europe is the great development of white chalk in the Anglo-French area, and its grad ual replacement, when following E. into Germany, etc., by earthy limestones, shales, sandstones, etc. The most marked characteristic of the Cretaceous system in southern Europe is the great de velopment in that region of massive ma rine limestone (hippurite limestone).
In North America Cretaceous strata likewise occur, especially in the Western States and Territories. They also oc cupy wide tracts in the Gulf States, whence they extend up the Mississippi Valley to the Ohio; they put in appear ance at intervals on the Atlantic bor der between South Carolina and New Jersey, and are met with again on the Pacific border and in the coast-range. Strata of the same age occur also in the far W. of Canada, at the mouth of the Mackenzie river, and in Green land. In India the system is marked in the Deccan by a massive series of basalt-rocks 4,000 to 6,000 feet thick, and covering an area of 200,000 square miles. In Australia and New Zealand there is a considerable development of these rocks, such as the "desert sandstones" of Queensland, and a small coal-bearing group of beds. In New Zealand, the
system contains coals, some of which are lignites while others are bituminous of fair quality. The Wealden Beds con sist largely of clay and sand, and are almost entirely of fresh-water origin. In Yorkshire, however, the strata which occur on the same horizon as the Weal den Beds of the S. are of marine origin, as seen in the Speeton clay near mid lington. The Lower Greensand, consist ing of sand, clay, etc., is marine. The gault, a tough blue clay, is likewise ma rine, and so also are the shallow-water sands of the Upper Greensand, and the thin layer of chalky marl called Chlo ritic Marl. The most characteristic rocks of the system are the chalk beds.
The Cretaceous strata of Great Brit ain being almost exch:sively of marine origin, it is not surprising that land plants seldom occur, and that they are met with chiefly in the fresh-water beds near the base of the system. They con sist chiefly of ferns, cycads, and conifers, a flora resembling that of the preceding Jurassic period. The Upper Cretaceous rocks of Germany, however, have fur nished many plant remains. Among those are the oldest known dicotyledons, such as extinct species of maple, oak, walnut, beech, laurel, magnolia, etc., also several proteaceous plants. A similar admixture of forms occurs in the Cre taceous strata of North America. Among animals the protozoa played a very im portant part—the white chalks and earthy limestones being very largely composed of the minute shells of fora minifera, such as globigerina, rotalia, and textularia. which still swarm in the ooze of the Atlantic. Ordinary bivalves were also very numerous. In the Da nian beds carnivorous gasteropods begin to abound, and they include a number of existing genera. Cephalopods are not only the most abundant, but also the most characteristic fossils of the Cre taceous rocks. Among the fishes were ganoids, and various kinds of the shark tribe, together with the earliest repre sentatives of the teleostei, which include most living genera of fishes. The waters of the period seem also to have swarmed with reptiles, such as the ichthyosaurus and plesiosaurus. Winged reptiles were also present, such as pterodactylus.