Farther down still he finds the trunks of the _Pinus sylvestris_, or
Scotch fir, together with implements of stone. This clearly indicates
that in the lapse of centuries the pine was supplanted by the oak, and
the oak by the beech, and that man advanced contemporaneously from the
knowledge and use of stone implements to those of bronze and iron. Now
the known fact is that in the time of the Romans, as now, the Danish
isles were covered by magnificent beech forests, and that eighteen
centuries have done little or nothing toward changing the character of
the vegetation. How many centuries must have elapsed to enable the oak
to supplant the pine, and the beech to supplant the oak, can only be
vaguely conjectured. Yet the evidence is clear that man lived in those
old pine forests--leaving his implements of stone behind him, as he did
his tools of bronze and iron in the succeeding periods. Along the coast
of Denmark, also, are found shell mounds mixed with flint knives,
hatchets, etc., but never any tools of bronze or iron, showing that the
rude hunters and fishers who fed on the oyster, cockle, and other
mollusks, lived in the period of the Scotch fir, or, as it has been
called, the 'age of stone.'

In many of the Swiss lakes are found ancient piles driven into the
bottom, on which were once erected huts or villages, the lacustrine
abodes of man. This use of them is proved by the abundance of flint
implements and fragments of rude pottery, together with bones of
animals, which have been dredged up from among the piles. The implements
found belong to the 'age of stone,' or the period of the Scotch fir in
Denmark, and the bones of animals are all, with one exception, those of
living species.

Passing over the fossil human remains and works of art of the 'recent'
period, as found in the delta and alluvial plain of the Nile, in the
ancient mounds of the valley of the Ohio, in the mounds of Santos in
Brazil, in the delta of the Mississippi, in which, at the depth of
sixteen feet from the surface, under four buried forests, superimposed
one upon the other, was found, a few years ago, a human skeleton,
estimated by Dr. B. Dowler to have been buried at least fifty thousand
years--in the coral reefs of Florida, in which fossil human remains were
found, estimated by Professor Agassiz to have an antiquity of ten
thousand years--in the recent deposits of seas and lakes, in the central
district of Scotland, which bears clear traces o