The native metallurgist had learned the art of alloying his ductile copper with the still softer tin, and producing by their chemical admixture a harder, tougher metal than either. But he does not appear to have carried his observation so far as to ascertain the most efficient proportions of the combining metals; or even to have made any very definite approximation to a fixed rule, further than to use with great moderation the alloying tin. He had discovered, but not entirely mastered, a wonderful secret, such as in the ancient world had proved to lie at the threshold of all higher truths in mechanical arts. He was undoubtedly advancing, slowly but surely, on the direct course of national elevation; and the centuries which have followed since the conquests of Cortes and Pizarro might have witnessed in the New World triumphs not less marvellous in the progress of civilisation than those which distinguish the England of Victoria from that of the first Tudor. But native science and art were abruptly arrested in their progress by the Spanish conquistadors; and it is difficult to realise the conviction that either Mexico or Peru has gained any adequate equivalent for the loss which thus debars us from the solution of some of the most interesting problems connected with the progress of the human race. Amid all the exclusiveness of China, and the isolation of Japan, there is still an unknown quantity among the elements of their civilisation derived from the same sources as our own. But the America of the fifteenth and sixteenth centuries was literally another world, securely guarded from external influences. Nevertheless while all appears to have been self-originated, we meet everywhere with affinities to the arts of man elsewhere, and trace out the processes by which he has been guided, from the first promptings of a rational instinct to the intelligent development of many later steps of reason and experience. ----- [78] _Méms. Chemical Society_, vol. iv. p. 288. [79] _Edinburgh Philosophical Journal_, vol. vi. p. 357. [80] _Prehistoric Annals of Scotland_ (2d ed.), vol. i. p. 319. [81] _Proceedings_, _B. N. H. S._, vol. v., p. 63. [82] Anahuac, p. 153. CHAPTER X. THE MOUND-BUILDERS. EARTH-PYRAMIDS—MONUMENTS OF THE MOUND-BUILDERS—SEATS OF ANCIENT POPULATION—DIFFERENT CLASSES OF WORKS—ANCIENT STRONGHOLDS— NATURAL SITES—FORT HILL, OHIO—IROQUOIS STRONGHOLDS—ANALOGOUS STRONGHOLDS—FORTIFIED CIVIC SITES—SACRED ENCLOSURES—NEWARK EAGLE MOUND—GEOMETRICAL EARTHWORKS—PLAN OF NEWARK EARTHWORKS, OHIO—A STANDARD OF MEASUREMENT—DIVERSITY OF WORKS—THE CINCINNATI TABLET—A GEOMETRICAL INSTRUMENT—TRACES OF EXTINCT ARTS.