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vii THE ANTIQUITY AND ORIGIN OF MAN 425The island containing these remarkable works of art hasonly an area of about thirty square miles, or considerably lessthan Jersey. Now, as one of the smallest images (eight feethigh) weighs four tons, the largest must weigh over ahundred tons, if not much more ;and the existence of suchvast works implies a large population, abundance of food, andan established government. Yet how could these coexist ona mere speck of land wholly cut off from the rest of theworld ? Mr. Mott maintains that these facts necessarilyimply the power of regular communication with larger islandsor a continent, the arts of navigation, and a civilisation muchhigher than now exists in any part of the Pacific. Verysimilar remains in other islands scattered widely over thePacific add weight to this argument.North American EarthworksThe next exampleis that of the ancient mounds andearthworks of the North American continent, the bearing ofwhich is even more significant. Over the greater part of theextensive Mississippi valley, four well-marked classes of theseearthworks occur. Some are camps, or works of defence,situated on bluffs, promontories, or isolated hills ;others arevast inclosures in the plains and lowlands, often of geometricforms, and having attached to them roadways or avenuesoften miles in length ;a third are mounds corresponding toour tumuli, often seventy to ninety feet high, and some ofthem covering acres of ground while a fourth ;group consistsof representations of various animals modelled in relief on agigantic scale, and occurring chiefly in an area somewhat tothe north-west of the other classes, in the plains of Wisconsin.The first class the camps or fortified inclosures resemblein general features the ancient camps of our ownislands, but far surpass them in extent. Fort Hill, in Ohio,is surrounded by a wall and ditch a mile and a half in length,part of the way cut through solid rock. Artificial reservoirsfor water were made within it,while at one extremity, on amore elevated point, a keep is constructed with its separatedefences and water-reservoirs. Another, called Clark's Work,in the Scioto valley, which seems to have been a fortifiedtown, incloses an area of 127 acres, the embankments measur-