IN THE THAMES BASIN. 109
this remarkable fauna: the one is now a purely Arctic animal,
and the other survives only in Scandinavia.
Two more voles, the bison and bear, complete the list, while
the beaver, urus, reindeer, wolf, and another species of bear,
which appear to have lived on into the succeeding Neolithic
period, must also be mentioned as interesting members of
the Palaeolithic fauna.
Of the invertebrates there is at least one extinct species of an
Ostracod, a Pelecypod, and a Gastropod, while there are several
which, though still living on the European mainland, are no
longer inhabitants of Britain.
A complete review of the previous literature relating to the
valley drifts of the lower Thames Basin is given by Whitaker in
The Geology of London (Memoir Geol. Survey: 1889). This is
brought up to date in his Address to the Geologists' Association
in 1901.
A tolerably complete list of the invertebrate remains occurring
in these beds will be found in the following papers:—W. J.
Lewis-Abbott, "The Sections exposed in the foundations of the
New Admiralty Offices," Proc. Geologists' Assoc. xii., 1892. J. P.
Johnson and G. White, "Some new Sections in, and contributions
to the Fauna of, the River Drift of Ilford," and J. P. Johnson,
"Additions to the Palaeolithic Fauna of the Uphall Brickyard,
Ilford," Essex Naturalist xi., 1899-1900. Hinton and
Kennard, "Contributions to the Pleistocene Geology of the
Thames Valley," Part I., Essex Naturalist, xi., 1900.
Kennard and Woodward, " Post-Pliocene Non-Marine Mollusca
of the South of England," Proc. Geologists' Assoc. xvii., 1901
(Wartford, Swanscombe, Crayford, and Erith, Green-Street-
Green).
Between the laying down of the last of the valley-drifts and
the commencement of the deposition of the next series of
deposits—the alluvial flats—a great interval of time must have
elapsed, an interval sufficient to permit of the extinction or
migration elsewhere of the remarkable assemblage of mammals
enumerated above, and to allow of the replacement of the
characteristic Palaeolithic implements by others of a totally
different type.
The newest series of fluviatile deposits in the Thames Basin
—the beds of clay, mud, and peat which make up the alluvial