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-eartli. 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 
fiuminalis . 8 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 w r as once very much wider 
over Europe than at present. It no doubt indicates a great 
Fig. 4.—The Musk-Ox (Ovibos moscliatus), 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 hrick-eartli w r e become 
acquainted with a land-fauna of wdiicli 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 , Caill. Voy. Egypt, 2, t. 61, fig. 10, 11. Morris, 
- Cat. Brit. Foss., 1854, p. 199.—Grays, Ilford, Erith. 
