40 INVERTEBRATE ANIMALS. 
DISTRIBUTION OF FORAMINIFERA IN TIME.—It is not the object of 
the present work to enter into the consideration of the past existence of 
different groups of animals, since this presupposes some knowledge of 
geology, but the Foraminifera present some points of special interest 
which may be very shortly noticed. In the first place, as far as is yet 
known, the vraminifera were the earliest and oldest of created beings. 
The oldest fossil which has hitherto been exhumed by the labours of 
geologists is believed to have been a Foraminifer,* of large size, and 
with some decided affinities to existing forms. In the second place, it is 
only by an examination of the distribution of the Foraminifera in past 
time that we can arrive at any adequate notion of the importance of 
these microscopic creatures when looked atin the aggregate. The great 
geological formation known as the white chalk—a formation which forms 
the well-known chalk-cliffs of the south of England, and which stretches 
over a great part of the continent of Europe, attaining sometimes a 
thickness of not less than 600 feet—is almost wholly composed of the 
shells of Foraminifera, visible only to the microscope. The smallest 
fragment of the common chalk, with which every one is familiar, con- 
tains numbers of these minute shells ; and it is a singular fact that some 
of the species in the chalk are indistinguishable from forms which now 
occur in the ooze which forms the bed of the Atlantic at great depths. 
The stone of which Paris is built is to a very great extent composed of 
the shells of Foraminifera, especially of the A@z/co/a ; and it is hardly an 
exaggeration to say that Paris is mainly built up out of these minute 
organisms, Another remarkable formation is that known as the *‘ Num- 
mulitic limestone,” from the presence in it of a large coin-shaped Fora- 
minifer, the Nummulite (fig. 7), generally about as large as a shilling. 
Fig. 7.—Nummutlites levigatus. 
The Nummulitic limestone stretches from France on the west to the 
frontiers of China on the east, and is almost everywhere readily recog- 
nisable as a distinct formation. It attains in places a thickness of seve- 
ral thousand feet, and is especially largely developed in the Alps. It 
has an historic interest from the fact that the Pyramids are built of it, 
and that the Nummulites in it were noticed by Herodotus, ‘‘ the father 
of history.” 
* The Zogoéx Canadense of the Laurentian Rocks of Canada. 
