THE) CARBONIFEROUS PERIOD. t7* 
have been formed in inland swamps and morasses, or in brack- 
ish-water lagoons, creeks, or estuaries. A corresponding dif- 
ference exists necessarily in the animal remains of these de- 
posits, and in many regions this difference is extremely well 
marked and striking. The great marine limestones which 
characterise the lower portion of the Carboniferous series in 
Britain, Europe, and the eastern portion of America, and the 
calcareous beds which are found high up in the Carboniferous 
in the western States of America, may, and do, often contain 
the remains of drifted plants ; but they are essentially charac- 
terised by marine fossils; and, moreover, they can be demon- 
strated by the microscope to be almost wholly composed of 
the remains of animals which formerly inhabited the ocean. 
On the other hand, the animal remains of the beds accompany- 
ing the coal are typically the remains of air-breathing, terres- 
trial, amphibious, or aerial animals, together with those which 
inhabit fresh or brackish waters. Marine fossils may be found 
in the Coal-measures, but they are invariably confined to spe- 
cial horizons in the strata, and they indicate temporary depres- 
sions of the land beneath the sea. Whilst the distinction bere 
mentioned is one which cannot fail to strike the observer, it is 
convenient to consider the animal life of the Carboniferous as 
a whole: and it is simply necessary, in so doing, to remember 
that the marine fossils are in general derived from the inferior 
portion of the system; whilst the air-breathing, fresh-water, and 
brackish-water forms are almost exclusively derived from the 
superior portion of the same. 
The Carboniferous Profozoans consist mainly of Foramini- 
fera and Sponges. The latter are still very insufficiently known, 
but the former are very abundant, and belong to very varied 
types. Thin slices of the limestones of the period, when ex- 
amined by the microscope, very commonly exhibit the shells 
of Foraminifera in greater or less plenty. Some lmestones, 
indeed, are made up Of little else than these minute and elegant 
shells, often belonging to types, such as the Textularians and 
Rotalians, differing little or not at all from those now in exist- 
ence. This is the case, for example, with the Carboniferous 
Limestone of Spergen Hill in Indiana (fig. 114), which is 
almost wholly made up of the spiral shells of a species of 
Endothyra. In the same way, though to a less extent, the 
black Carboniferous marbles of eld. and the similar mar- 
bles of Yorkshire, the limestones of the west of England and 
of Derbyshire, and the great “Scar Limestones” of the north 
of England, contain great numbers of Foraminiferous shells ; 
whilst similar organisms commonly occur in the shale-beds 
