In 1875 I devoted several weeks to a careful study of some of the principal groups of ancient earthworks in the Ohio valley, and visited Flint Ridge to examine a group of native flint pits in the old Shawnee territory. The Shawnees were formerly a numerous and powerful tribe of Indians; but they took part, in 1763, in the conspiracy of Pontiac, and were nearly exterminated in a battle fought in the vicinity of their old quarries. From these it is probable that the older race of Mound-Builders of the Ohio valley procured the material from which they manufactured many of their implements, including some of those used in the construction of their great earthworks. Flint Ridge, as the locality is called, a siliceous deposit of the Carboniferous age, extends through the State of Ohio, from Newark to New Lexington. It has been worked at various points in search of the prized material; and the ancient pits can still be recognised over an extensive area by the funnel-shaped hollows, or slighter depressions where the accumulated vegetable mould of many winters has nearly effaced the traces of the old miners. The chert, or hornstone, of this locality accords with that from which the implements recovered from the mounds appear to have been chiefly made. One fact which such disclosures place beyond doubt, namely, that the so-called Mound-Builders had not advanced beyond the stage of flint or stone implements, is of great significance. Their numbers are proved by the extent of their earthworks in many localities in the Ohio valley; and the consequent supply of implements needed by them as builders must have involved a constant demand for the flint-miners and tool-makers. The great earthworks at Newark are among the most extensive structures of this class, covering an area of several miles, and characterised by the perplexing element of elaborate geometrical figures, executed on a gigantic scale by a people still in the primitive stage of stone implements, and yet giving proof of skill fully equalling, in the execution of their geometrical designs, that of the scientific land-surveyor. On this special aspect of the question, it may be well to revert to notes written immediately after a careful survey of the Newark earthworks, so as to suggest more clearly their extent and the consequent number of workmen and of tools in demand for their execution. The sacred enclosures have to be classed apart from the military works of the Mound-Builders. Their elaborate fortifications occupy isolated heights specially adapted for defence, whereas the broad river-terraces have been selected for their religious works. There, on the great unbroken levels, they form groups of symmetrical enclosures, square, circular, elliptical, and octagonal, connected by long parallel avenues, suggesting analogies with the British Avebury, the Breton Carnac, or even with the temples and sphinx-avenues of the Egyptian Karnak and Luxor; but all wrought of earth, with the simple tools made