EASTERN BRITISH PLIOCENES.
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much speculation as to origin and introduction, and I propose
to briefly discuss the question.
These exotics comprise many igneous rocks, such as granite,
porphyry, quartzites, etc. ; rocks and fossils chiefly Secondary
and Cretaceous, from a distance, and others of Eocene and
later date, from nearer at hand ; fossils from the London Clay
such as bones, teeth or scutes of Hyracotherium, Coryphadon,
Crocodiles, Turtles, with many Fish and Crustacea ; phos-
phatised bones, teeth, otolites and snouts of Ziphoid and other
Cetaceans abound ; terrestrial Mammalia, and as will be noted
in the sequel, numerous shells of Miocene and Early Pliocene
origin. These, with the phosphatic nodules or so called Coprolites,
the boxes or box stones, at times containing fossils, and much
wood, complete the list.
Many of the terrestrial vertebrate remains are highly phos-
phatized, yet from their often perfect preservation and condition
they may represent the land fauna of the period, however they
may have got into the marine area.
If, as Prof. Bonney remarks, these phosphatic nodules may
be formed by segregation out of mud saturated by phosphate
of lime, then the Coprolites or phosphatic nodules, which
often contain sixty per cent. of this mineral, may be of any age ;
some of them in the Ipswich and other museums certainly enclose
Graphularia, shells and fish teeth, and the London Clay fishes
and crustacea are little else than masses or lumps of phosphate.
Although scattered upon the surface of the London Clay, these
latter are not found in situ, but are exotics, like the others coming
from, I would suggest, a former extension of the Sheppy area,
where these abounded at one time.
These derivates are not, as commonly supposed, found
only at the bottom or basement of the Crag, or forming the Crag
floor. They occur not only there, but also in less abundance
throughout the strata in some of the Red Crag beds, especially
in the Newbournian zone ; their greater abundance at the lower
or basement position is probably due to their heavier specific
gravity, as in the shifting sands they would naturally find a
lower level, inasmuch as we find the exotic shells intermixed
with the proper species of the seas, as I shall point out in due
season, their specific gravity being about the same.
The "box stones" (or "boxes," as the workmen call the