10 The Ancient Fauna of Essex.
fresh-water Mollusca, and the bones of land animals. These
deposits are well seen at Ilford, and similar deposits are found
at Crayford, Erith, and Grays. In these older deposits it
will be seen that the Thames Valley gravel overlies the
yellow sand and brick-earth. The age of these yellow sands
and clayey brick-earths is very well marked, for they every-
where contain that most characteristic bivalve shell—Cyrena
fluminalis* It is excessively interesting to note that this
little mollusk is now known only as an inhabitant of the
River Nile, so that its distribution was once very much wider
over Europe than at present. It no doubt indicates a great
Fig. 4.—The Musk-Ox (Ovibos moschatus), now only found living on the
treeless barrens of Arctic America and Asia. It was shot on North
Grinnell Land during the last Arctic voyage of the 'Alert' and 'Discovery.'
Its remains have been found at Maidenhead ; at Green Street Green, in
Kent ; at Crayford ; and Grays. [Reproduced, by permission, from the
Guide Book to the Geological Department in the British Museum of
Natural History.]
geological and climatic change, and most certainly marks the
lapse of a long period of time. In the brick-earth we become
acquainted with a land-fauna of which only a stray form or
two now exist. Thanks to the researches of Sir Antonio
Brady and others, we are able to record from these brick-
8 Cyrena consobrina, Gaill. Voy. Egypt, 2, t. 61, fig. 10, 11, Morris,
Cat. Brit. Foss., 1854, p. 199—Grays, Ilford, Erith.