Some limestones, 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 existence. 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 Ireland, and
the similar marbles 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
associated with the limestones throughout the Lower Carboniferous
series. One of the most interesting of the British Carboniferous
forms is the _Saccammina_ of Mr Henry Brady, which is sometimes
present in considerable numbers in the limestones of Northumberland,
Cumberland, and the west of Scotland, and which is conspicuous
for the comparatively large size of its spheroidal or pear-shaped
shell (reaching from an eighth to a fifth of an inch in size).
More widely distributed are the generally spindle-shaped shells
of _Fusulina_ (fig. 115), which occur in vast numbers in the
Carboniferous Limestone of Russia, Armenia, the Southern Alps,
and Spain, similar forms occurring in equal profusion in the
higher limestones which are found in the Coal-measures of the
United States, in Ohio, Illinois, Indiana, Missouri, &c.
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