That the Mound-Builders and their works belong to a distant period in
the past is evident; but, of course, we have no means of determining
their antiquity with any approach to accuracy, no scheme of chronology
by which their distance from us in time can be measured. Nevertheless,
some things observed in their remains make it certain that the works are
very ancient.
1. One fact showing this is pointed out by those who have examined them
carefully as follows: None of these works (mounds and inclosures) occur
on the lowest-formed of the river terraces, which mark the subsidence of
the western streams; and as there is no good reason why their builders
should have avoided erecting them on that terrace, while they raised
them promiscuously on all the others, it follows, not unreasonably, that
this terrace has been formed since the works were erected. It is
apparent, also, that in some cases the works were long ago partly
destroyed by streams which have since receded more than half a mile, and
at present could not reach them under any circumstances. Those streams
generally show four successive terraces, which mark four distinct eras
of their subsidence since they began to flow in their present courses.
The fourth terrace, on which none of the works are found, marks the
last and longest of these periods; and it marks also the time since the
Mound-Builders ceased to occupy the river-valleys where it was formed.
The period marked by this fourth terrace must be the longest, because
the excavating power of such streams necessarily diminishes as their
channels grow deeper. This geological change, which has taken place
since the latest of the mounds and inclosures were constructed, shows
that the works are very old; no one can tell how old. To count the years
is impossible; but we can see that the date, if found, would take us
back to a remote period in the past.
2. Great antiquity is indicated by the skeletons taken from the mounds.
Every skeleton of a Mound-Builder is found in a condition of extreme
decay. It sometimes appears that the surface of a mound has been used by
the wild Indians for interments; but their skeletons, which are always
found well preserved, can be readily distinguished by their position in
the mounds, as well as by other peculiarities. The decayed bones of
Mound-Builders are invariably found within the mounds, never on the
surface, usually at the bottom of the structure, and nearly always "in
such a state of decay as to render all attempts to restore the skull,
or, indeed, any part of the skeleton, entirely hopeless." Not more than
one or two skeletons of that people have been recovered in a condition
suitable for intelligent examination. It is stated in the work of Squier
and Davis that the only skull belonging incontestably to an individual
of the Mound-Building race, which has been preserved entire, was taken
from a mound situated on a knoll (itself artificial apparently) on the
summit of a hill, in the Scioto Valley, four miles below Chillicothe.
What, save time itself, can have brought these skeletons to a condition
in which they fall to pieces when touched, and are ready to dissolve and
become dust? All the circumstances attending their burial were unusually
favorable for their preservation. The earth around them has invariably
been found "wonderfully compact and dry." And yet, when exhumed, they
are in such a decomposed and crumbling condition that to restore them is
impossible. Sound and well-preserved skeletons, known to be nearly two
thousand years old, have been taken from burial-places in England, and
other European countries less favorable for preserving them. The
condition of an ancient skeleton can not be used as an accurate measure
of time, but it is sufficiently accurate to show the difference between
the ancient and the modern, and in this case it allows us to assume that
these extremely decayed skeletons of the Mound-Builders are much more
than two thousand years old.
Those familiar with the facts established by geologists and
palaeontologists are aware that remains of human skeletons have been
discovered in deposits of the "Age of Stone" in Western Europe; not to
any great extent, it is true, although the discoveries are sufficient to
show that fragments of skeletons belonging to that age still exist. It
is not without reason, therefore, that the condition of decay in which
all skeletons of the Mound-Builders are exhumed from their burial-places
is considered a proof of their great antiquity. There is no other
explanation which, so far as appears, can be reasonably accepted.
3. The great age of these mounds and inclosures is shown by their
relation to the primeval forests in which most of them were discovered.
I say _primeval_ forests, because they seemed primeval to the first
white men who explored them. Of course there were no unbroken forests at
such points as the Ohio Valley, for instance, while they were occupied
by the Mound-Builders, who were a settled agricultural people, whose
civilized industry is attested by their remains. If they found forests
in the valleys they occupied, these were cleared away to make room for
their towns, inclosures, mounds, and cultivated fields; and when, after
many ages of such occupation, they finally left, or were driven away, a
long period must have elapsed before the trees began to grow freely in
and around their abandoned works. Moreover, observation shows that the
trees which first make their appearance in such deserted places are not
regular forest trees. The beginning of such growths as will cover them
with great forests comes later, when other preliminary growths have
appeared and gone to decay.
When the Ohio Valley was first visited by Europeans it was covered by an
unbroken forest, most of the trees being of great age and size; and it
was manifest that several generations of great forest trees had preceded
those found standing in the soil. The mounds and inclosures were
discovered in this forest, with great trees growing in them. Eight
hundred rings of annual growth were counted in the trunk of a tree
mentioned by Sir Charles Lyell and others, which was found growing on a
mound at Marietta. In the same way, successive generations of forest
trees had grown over their extensive mining works near Lake Superior,
and many of those works are still hidden in what seem to be primeval
forests.
General Harrison made the following suggestion in regard to the
establishment of these forests in Ohio. When the individual trees that
first got possession of the soil had died out one after another, they
would, in many cases, be succeeded by other kinds, till at last, after a
great number of centuries, that remarkable diversity of species
characteristic of North America would be established. His suggestion,
the result of practical observation and study, is not without reason. It
is certain, in any case, that the period when these old constructions
were deserted is so far back in the past, that sufficient time has since
passed for the abandoned towns and fields to remain for years, and
perhaps centuries, as waste places, pass through the transition from
waste lands to the beginning of forest growths, and then be covered by
several generations of such great forest trees as were cleared away to
prepare the soil for the settlements, towns, and farms of our people.