In this case they constructed a sort of a cave, but in many cases they mined open to the air, that is, they simply dug trenches or pits. A row of these ancient pits, now slight depressions, indicate a vein. What they seem to have especially sought after was lumps of copper that they could easily manage and fashion by hammering. They had not discovered the art of melting. When they found an unusually large piece, they broke off what they could by vigorous hammering. In one case they found a mass weighing about six tons of pure copper. They made an attempt to master this piece. By means of wedges they had got it upon a cob-work of round logs or skids, six or eight inches in diameter, but the mass was finally abandoned for some unknown reason after breaking off such pieces as they could until the upper surface was smooth. This mass rested on the framework of logs while the years came and went, until, after the lapse of unknown time, the white men once more opened the old mine. On the rubbish in front of this mine was standing the stump of a pine tree ten feet in circumference. These ancient mines are found not only on the main-land, but on the islands off the coast as well. The only helps they seem to have employed was fire, traces of which are found everywhere, and stone mauls and axes. The mauls consist of oblong water-worn bowlders of hard tough rock, nature having done every thing in fashioning them except to form the groove, which was chiseled out around the middle. Some copper implements were also found. Col. Whittlesey, from whose writings we have drawn the foregoing, concludes that these mines were worked by the Mound Builders. As he finds no traces of graves or houses, or other evidence of a protracted stay, he thinks they were worked only through the Summer season of the year by bands of workmen from the south. As to what caused the abandonment of the works we do not know. It might have been an impulse of their race hurrying them on to some distant migration; or, more probably, pressed by foes from without, they were compelled to abandon their ancient homes. Whatever the cause was, nature resumed her sway. Forest trees crept up to and grew around the mouths of the deserted mines. Col. Whittlesey concludes from the group of trees growing on the top of the rubbish heap that at least five hundred years passed away before the white man came from the south to resume the work of his ancient predecessor.90