If palaeolithic or rudely chipped implements are the oldest known, as they not improbably were the first tools used by man, yet their use has extended in the case of rude nations all the way up to the present time; and in America and Northern Asia we know that their antiquity is but of yesterday, and that they were used with highly finished implements of bone, and of those softer stones that admit of being polished. No certain line can therefore be drawn even locally between a Neolithic and a Palaeolithic period, especially since in localities where flint implements were extensively quarried and made, as on the banks of rivers in Northern France and Southern England, and in such places as "Grimes' Graves" and Cissbury in the latter country, where mines were sunk in the chalk for the extraction of flints, it necessarily happened that vast multitudes of unfinished or spoiled implements and weapons were left on the ground, while the better-formed specimens were for the most part taken away. This conclusion is amply supported by similar localities in America, where people well acquainted with many of the arts of life have left quantities of strictly palaeolithic material. Wilson, Southall, and other writers have accumulated so many examples of this that I think the distinction of Palaeolithic and Neolithic ages must now be given up by all investigators who possess ordinary judgment. A remarkable instauce is the celebrated "Flint ridge" of Ohio, which was a great quarry of flint for implements used by the ancient mound-builders, a highly civilized race, as well as by the modern Indians. Here are found countless multitudes of palaeolithic flint implements of all the ordinary types, but which are merely the unfinished material of workers capable of producing the most exquisite implements. There can be scarcely a doubt that the palaeolithic implements of the European gravels, in so far as they are the workmanship of man, are in like manner merely the relics of old flint quarries.[120]