Later Beds of the Glacial Formation. ral 
exceptions, agree perfectly with those now inhabiting our 
southern coasts. 
6. From the fossil species we may infer that in the ear- 
lier post pliocene period a more northern fauna occupied 
our southern coasts than now prevails there ; in other words, 
such a fauna as now exists only in the arctic zone. On the 
other hand, in the later period indicated by the newer beds, 
the arctic species gradually retired to the far north, and 
were replaced by the more southern forms, which now con- 
stitute so large a part of our marine fauna. 
Loven, in his “Ofversigt af Ventensk. Akad. Forh., 1846,” 
p. 204, has also arrived at a similar conclusion from an 
examination of the fossil mollusca in the neighbourhood of 
the west coast.of Sweden ; with this difference, however, 
that, according to him, “ the arctic species present them- 
selves at those spots which are furthest from the coast, 
while the nearer any locality is to the shore, the rarer are 
the arctic species, these being gradually replaced by more 
southern species.” Whereas, with us, mere distance from 
the coast does not afford a test of the age of a fossil, and 
the older or arctic species are found in the shell-beds at the 
greatest heights above the sea, and in the clay furthest 
below the surface, independent of distance from the coast. 
[This view is remarkably confirmed by the Hlie shell-bed 
described by the Rev. Thomas Brown, F.R.S.E., in his 
paper read before the Royal Society Edinburgh, March 2, 
1863. Translator. | 
7. Finally, two species have been noticed, viz. Trochus 
magus (in the older beds), and Tapes decussata (in the later 
beds), and to these, perhaps, should be added Pholas 
candida, which no longer inhabit our coasts, but are dis- 
tributed from the Mediterranean to England. In regard to 
these species, we can only conjecture that in the Post- 
pliocene epoch they reached Norway, not from England 
but from the Mediterranean, between which and the North 
Sea a communication existed to the east of the Alps. 
Nor does this fact stand alone. I have already else- 
where called attention to two other indications of such a 
connection between these seas at an earlier period, vizi— 
the well known fact that some of the characteristically 
