e that the erratics--a name applied to boulders in
boulder-clay--in the upper division have travelled in a different
direction from those contained in the lower. Taking for granted that the
boulder-clay is a marine deposit, this phenomenon seems to indicate that
the current which prevailed during the early part of the Glacial period
in this North European ocean was different from the prevailing current
during the latter part. I have attempted to explain this circumstance by
the supposition that during the early part of the Glacial period the
Northern Sea had a connection with the Ponto-Caspian Sea--a sea formed
by the junction of the Black Sea and the Caspian (Fig. 12, p. 156).
There is geological evidence, as will be explained in the following
chapter, that the area of these two seas was considerably larger in
glacial times than it is now, and that they were joined across the
valley of the Manytch. After the inter-glacial phase of the Glacial
period, the North European Ocean became connected with the Atlantic
Ocean across the north of England (Fig. 6, p. 126), the junction between
the former and the Ponto-Caspian having meanwhile become dry land (Fig.
13, p. 170). A fresh current, now flowing westward, was set up in the
North European Ocean, which accounts for the fact just cited that the
erratics in the upper continental boulder-clay have travelled in a
different direction from those in the lower. The boulder-clay laid down
by the sea on the midland and northern counties of England, just as was
the case with the similar deposit on the Continent, is generally
accredited to the action of land-ice. It is by most geologists looked
upon as the ground-moraine, partly of the huge Scandinavian glacier
which is supposed to have impinged upon the English coast, partly of
local British glaciers.

But renewed geological investigations on this point throw doubts upon
these theories. Thus Mr. Harmer remarks in a recent contribution to
glacial literature (p. 775), that "it is difficult to see how the Baltic
glacier could have reached East Anglia, though ice-floes with
Scandinavian boulders might easily have done so, while had the Norwegian
ice filled the North Sea and overflowed the county of Norfolk, some
evidence of its presence ought to be found in the glacial beds of
Holland."

All the phenomena of distribution of the British fauna and flora are, as
we have seen, much more easily explained by the supposition of a damp,
tempera