68 
Britain, and the accumulation of the Coralline Crag and 
Passage beds of Walton-on-the-Naze, the fauna maintaining 
its Miocene or southern aspect, northern shells being entirely 
absent. In the next stage we have considerable alterations, 
hut also a large influx of northern species, these ultimately 
superseding the southern fauna. 
On the western side the Atlantic Miocene seas had their 
Pliocene development in the Cotentin and La Manche 
departments of N. France. In their joint memoir upon the 
Cretaceous and Tertiary deposits of these places, M. M. 
Viellard and Dollfus separate the Pliocenes into two—the 
Terebratula conglomerate, near St. George’s Bohon (also 
mentioned by Sir Charles Lyell, and Mr. Godwin-Austen), 
and the Marnes a Nassa, at Le Bosq. The conglomerate is 
related through Area diluvii and Terebratula ampulla, or 
grandis, to the Diestien Lenham beds; and the Le Bosq 
deposit to the Coralline Crag by its general facies, and the 
many species in common. Of 43 species determined from this 
horizon by Messrs. Deslongschamps, Hebert and myself, 28 
are known in the Suffolk Pliocenes and it is in this direction, 
notwithstanding the immense lapse of time involved, that I 
look for the cause or presence of the southern fauna in the 
Selsey beds. 
It may well be that the extension of the Pliocene sea into 
the before-mentioned St. Erth Valley, coincided with the 
basement beds of Walton-on-the-Naze, for in both places the 
faunal evidence is against the presumption that they were open 
to northern influence, the necessary physical changes to this 
end, although probably in motion, not being sufficiently 
advanced. When they were so, we find on either side of the 
country that the northern fauna began to make itself felt, the 
southern fauna gradually dying out as the northern took root. 
This we see not only in the later Pliocenes of East England, 
but also in the Wexford gravels, which I have assumed else¬ 
where to be pre-glacial, and in the drifts of Killiney Bay, 
Ireland, and the fossiliferous beds in the Isle of Man, in all 
which places Pliocene or southern shells are present. 
That some line of communication was open between the 
northern and mediterranean Seas is proved by the presence of 
