164 GEOGNOSY AND GEOLOGY. 
is entirely wanting in England; on the other hand, it occurs in extraordinary 
development in Germany. 
c. Keuper. (Marnes irisées; Red marls.) This group exhibits a 
considerable resemblance to the variegated sandstones, especially to the 
upper division. The principal rock species are clays, marls, and sandstones 
of various colors. Associated with these are quartz rock, ferruginous 
brown limestone, clay quartz, and many others; subordinate are gypsum, 
karstenite, rock salt, and coal. Where the group is complete three divisions 
inay be established. The lower, that of the loamy ccal and of rock salt, 
consists principally of slate clay, loam, and a highly fossiliferous sandstone 
(equisetum sandstone). The sandstone is of inconsiderable compactness, of 
an oil-green color running into grey, of thin or thick stratification, and 
frequently mixed with scales of mica. Among the fossils it contains, are 
species of equisetum, ferns, mollusca, fish, and reptiles. The clays also are 
tolerably rich in organic remains, especially in plants and shells. Among 
the latter Posidonia minuta is characteristic of the lower division; remains 
of fish and reptiles are found in marl clay and clay marl. These principal 
masses are frequently accompanied by ferruginous brown limestone, 
dolomite, and cement stone, and contain loam coal, in which a good deal of 
‘pyrites is disseminated: gypsum, karstenite, and rock salt are subordinate 
masses. The middle division, that of the variegated marls and gypsum, is 
principally composed of clay and clay marl. The clay occurs in the form 
of shale, marl clay, and loam, frequently containing nodules of pyrites and 
argillaceous carbonate of iron. The clay and lime marl are worthy of note 
on account of the minerals they contain: among these are iron pyrites, lying 
scattered in the most beautiful crystals, calcareous spar, quartz, verdigris. 
and mountain blue: remains of fish and reptiles with the coprolites 
(petrified excrement) of the latter, characterize the fossil fauna. Accom- 
panying masses are clay quartz, quartz rock, and dolomite: subordinate are 
karstenite and gypsum. | 
Sandstones prevail in the upper division, both fine-grained clay sandstones 
and quartzose. ‘The argillaceous sandstone is of various colors of grey, red. 
and violet, producing the most diversified markings by their combinations. 
It contains vegetable remains, on which account it has been called rush 
sandstone. ) 
The quartzose sandstone of yellow bluish or ferruginous color is 
occasionally dotted with white feldspathic particles, and sometimes includes 
pieces of silicified wood. Another sandstone with an _ argillaceous, 
calcareous, or marly cement, is of very coarse grain, giving to it the 
appearance of a conglomerate: it is this which has been named arcose by 
Brogniart. A clay, marl clay, or slate clay often occupies the rank of a 
principal member, although it must be included among the subordinate : it 
also contains the same Posidonia minuta which characterizes the lower 
division. 
The Keuper is generally wel! stratified. The dolomite and magnesian 
limestone have a conspicuous secondary cleavage, often giving rise to the 
{ormation of caves. The thickness of this group amounts to about 1200 
594 
