176 .GEOGNOSY AND GEOLOGY. 
devour a Dapedium politum, e; c, a Plesiosaurus dolichodeirus ; and d, two 
Pterodactyles fighting. At the bottom of the water are Pentacrinites, Hf, 
Mollusca, Crustacea, skeletons of various animals. Ammonites and Nautili 
sail about on the surface with outspread mantle. The shores are lined with 
Cycadites, Conifere, Zamia, &c. 
Pl. 42, fig. 31, represents Gryphea incurva ; fig. 30, part of the jaw of a 
crocodile ; fig. 29, Pholadomya murchinsonii ; fig. 28, Ammonites walcotii ; 
fig. 27, a dorsal vertebra of Ichthyosaurus communis ; fig. 26, Clypeus 
clunicularis ; fig. 25, Cidaris intermedia. : 
Cretaceous System. The petrographical character of the Cretaceous 
System is essentially different from that of the Jura. The chalk forms a 
highly characteristic feature, although it does not occur in all cases. In 
addition to chalk there are compact limestones, mar] clays, sandstones, sand 
beds, and conglomerates, containing gypsum, karstenite, rock salt, iron-stone, 
and coal, as subordinate masses. 
The cretaceous system exhibits different features in different localities, 
having reference not only to the petrographical character, but to the 
distribution of the fossils. Such deviations from the normal character in 
the latter respect are found in the Alps, the Carpathians, in Southern France, 
Spain, &c., which in all probability have been effected by climatic 
differences. Plants are not very numerous; the few that do exist belong 
both to land and marine forms; leaves of terrestrial dicotyledons frequently 
occur. Animal remains are found in great numbers, especially marine 
species, among which may be enumerated Corals, Sponges, Alcyonia., 
Siphonia, Echini, Crinoidea; more rarely shells, particularly Spherolites, 
Hippurites, Turrilites, and Ammonites, which here disappear from the stage 
of animal life. The reptiles have become more similar to the present forms. 
The cretaceous formation is divisible into two groups. 
a. Greensand (Grés vert), subdivisible again into two sections, the 
quadersandstein and the chalk marl. The quadersandstein consists of 
sandstones of very loose texture, occurring in some localities as sand beds. 
They are sometimes argillaceous, calcareous, or marly, sometimes ferruginous, 
or cemented by chalcedony : the colors are white, grey, and red ; the lighter 
appear to predominate. The grain of these sandstones is of various 
character, fine, coarse, or conglomeratic. The sandstones themselves are 
occasionally traversed by veins of quartz, which remain in the weathered 
rock as intersecting elevations, and contain tree stems and shells. The 
accompanying clay beds are marly, and of a bluish color. 
The lower regions of this formation are generally ferruginous, while the 
upper are of a greenish color, owing to the presence of chlorite. 
Subordinate masses are granular clay, iron-stone. blue when fresh, brown 
when weathered, sandy argillaceous spherosiderites occurring in nodules 
or their aggregations, stone coal, lignite, and bituminous wood. 
The second formation, that of the chalk marl, consists of various clays 
and marls, with limestones. The marls occur as flame marl, chalk marl, 
and as marl clay, or clay marl. 
The flame marl is sandy, coarsely earthy, and of various shades of grey 
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