In considering the various theories respecting the migrations of the aboriginal tribes, it is strange that traces of the same kind of encampments have not been found either in the North-West towards Asia, or in the southern parts of the valley of the Mississippi. It is difficult to understand how it happens that these works only occur within a comparatively confined region. Their actual geographical limits are contained within an area bounded approximately, towards the South, by the left bank of the river Ohio, from the neighbourhood of Cincinnati towards the West, to Wheeling towards the East, and not extending northwards beyond a line drawn from East to West through the centre of Ohio. Consequently it will be seen, upon making a reference to the map, that the works of the people called the Mound Builders, are situated within the southern division of the State including both banks of the Ohio river. These were their extreme limits, but the part of the country chiefly occupied by them has a much lesser area. It is evident from the positions of the earthworks, that the tribes which raised them thought it necessary to maintain their communications by water with the valley of the Ohio, and on the banks of that river they had several important fortifications or encampments. It is, however, upon the banks of the tributaries that fall into the Ohio from the North, that their settlements were most numerous, especially upon the Scioto, the Muskinghum and the streams entering those rivers near Newark and Chillicothe. The first earthwork that I visited was the great mound of Miamisburgh, which is situated upon the summit of high ground overlooking the valley of the Little Miami river. It was opened and examined in 1869, a few months before I saw it. In appearance and shape it resembled the largest of the Tumuli that were raised upon the plains of Troy, but the dimensions of this American mound are much greater. It is sixty-eight feet high, and has a circumference at the base of about eight hundred and thirty feet.