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.