ever, of
the many members of this group of animals which flourished in
Eocene times, are the "Nummulites" (_Nummulina_), so called from
their resemblance in shape to coins (Lat. _nummus_, a coin). The
Nummulites are amongst the largest of all known _Foraminifera_,
sometimes attaining a size of three inches in circumference;
and their internal structure is very complex (fig. 214). Many
species are known, and they are particularly characteristic of
the Middle and Upper of these periods--their place being sometimes
taken by _Orbitoides_, a form very similar to the Nummulite in
external appearance, but differing in its internal details. In
the Middle Eocene, the remains of Nummulites are found in vast
numbers in a very widely-spread and easily-recognised formation
known as the "Nummulitic Limestone" (fig. 10). According to Sir
Charles Lyell, "the Nummulitic Limestone of the Swiss Alps rises
to more than 10,000 feet above the level of the sea, and attains
here and in other mountain-chains a thickness of several thousand
feet. It may be said to play a far more conspicuous part than
any other Tertiary group in the solid framework of the earth's
crust, whether in Europe, Asia, or Africa. It occurs in Algeria
and Morocco, and has been traced from Egypt, where it was largely
quarried of old for the building of the Pyramids, into Asia Minor,
and across Persia by Bagdad to the mouths of the Indus. It has
been observed not only in Cutch, but in the mountain-ranges which
separate Scinde from Persia, and which form the passes leading
to Cabul; and it has been followed still further eastward into
India, as far as Eastern Bengal and the frontiers of China."
The shells of Nummulites have been found at an elevation of 16,500
feet above the level of the sea in Western Thibet; and the
distinguished and philosophical geologist just quoted, further
remarks, that "when we have once arrived at the conviction that
the Nummulitic formation occupies a middle and upper place in the
Eocene series, we are struck with the comparatively modern date to
which some of the greatest revolutions in the physical geography
of Europe, Asia, and Northern Africa must be referred. All the
mountain-chains--such as the Alps, Pyrenees, Carpathians, and
Himalayas--into the composition of whose central and loftiest parts
the Nummulitic strata enter bodily, could have had no existence
till after the Middle Eocene period. During that period, the
sea prevailed where the