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 palæontologists 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.