The fossils of the cretaceous formation are very different from those of the oölite, and are such as to show that it was deposited in deep seas. _Microscopic shells_ are often so abundant as to constitute a large proportion of the mass. _Zoöphytes_ are very numerous, such as sponges, corals, star-fishes (Fig. 35, _d e_), and a few crinoidea (_b_). Mollusks were also abundant, and cephalopoda, consisting of chamber-shells and belemnites (Fig. 36). The belemnite probably resembled the existing cuttle-fish; but the remains consist, in most cases, of a partially hollow calcareous substance (_b_), which was contained within the animal, and formed its skeleton. The chalk and greensand are largely developed in England; and the same formation, with different lithological characters, is found in great force flanking the principal mountain ranges of southern Europe, and extending into Asia. In this country the system commences with the greensand and friable limestones of New Jersey, and following the Alleghany range to its southern termination, it bends around into a north-western direction, and is continued into Missouri. 7. _The Tertiary System._--The tertiary strata embrace the formations from the cretaceous to the human era. They consist of clay, sand, sandstone, marl and limestone, and are distinguished from the lower rocks by being less consolidated; though the limestones are in some instances solidified, and resemble the strata of earlier origin. The tertiary strata are generally of less thickness than the older formations, and less continuous, being local deposits formed in lakes and estuaries. In a few instances they have been thrown into inclined positions, though in most cases they have been but slightly disturbed, and raised but a few hundred feet above the present level of the sea. The late tertiary strata seldom overlap the older, so as to indicate their relative ages by superposition. They have therefore been separated into groups according to the proportions of living and extinct species of shells which they are found to contain. The oldest tertiary or _Eocene formation_[A] contains only four per cent, of living species, the _Miocene_ contains seventeen per cent., the Pleiocene forty per cent., and the _Pleistocene_ ninety per cent. [A] _Eös_, dawn, and _kainos_, recent. The formation which commenced at _the dawn of the recent period_, containing but a small number of living species. Miocene (_meion_, less), less recent than the Pleiocene (_pleion_, more). Pleistocene (_pleistos_, most), most recent.