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via THE ANTIQUITY OF MAN IN NORTH AMERICA 435as well as from trained observers who are fully aware of theimportance of every additional fact and the weight of eachfresh scrap of evidence. Having by the kindness of MajorPowell, the able Director of the United States Geological Survey,been able to look into the evidence recently obtainedbearing on this question in the North American continent, Ibelieve that a condensed account of it will certainly prove ofinterest to English readers.The most certain tests of great antiquity, even though theyafford us no accurate scale of measurement, are furnished bysuch natural changes as we know occur very slowly. Changesin the distribution of animals or plants, modifications of theearth's surface, the extinction of some species and the introductionof others, are of this nature, and they are the morevaluable because during the entire historical period changesof this character are either totally unknown or of very smallamount. Let us then see what changes of this kind haveoccurred since man inhabited the North American continent.Ancient Shell MoundsThe shell heaps of the Damariscotta River, in Maine, are remarkablefor their number and extent. The largest of thesestretches for about half a mile along the shore, and is often sixor seven feet, and in one place twenty-five feet, in thickness.They consist almost exclusively of oyster shells of remarkablesize, frequently having a length of eight or ten inches, and sometimesreaching twelve or fourteen inches. They contain fragmentsof bones of edible animals, charcoal, bone implements, andsome fragments of pottery. The surface is covered to a depthof several inches with vegetable mould, and large trees grow onthem, some more than a century old. The special feature towhich we now call attention is "that at the present timeoysters are only found in very small numbers, too small tomake it an object to gather them ;and we were credibly informedthat they have not been found in larger quantitiessince the settlement in the neighbourhood. It cannot be supposedthat the immense accumulations now seen on the shoresof Salt Bay could have been made unless oysters had existedin very large numbers in the adjoining waters." x Here we1 Second Annual Report of Trustees of Peabody Museum, p. 18.