=Slavery.= Slavery existed, the slaves having been criminals, prisoners of war, public debtors, persons who sold themselves into slavery, and children. Slavery was never the birthright of any child born in ancient Mexico. Children born to a slave were free. Yet children could be sold into slavery and were often sold by their parents, mostly on account of poverty. There was one peculiar thing in slavery here. With the consent of the master the parents could substitute a younger child as it grew up for an older one sold into slavery, which substitution could go on down to the youngest child. Slavery must have been rather mild, as in the presence of four witnesses the precise services were prescribed when a child was sold, and a slave could have a family and even hold other slaves, and, as was stated, all his children were born free, the worst feature having been that slaves were liable to be sacrificed. =Industries.= Agriculture was in quite an advanced stage in ancient Mexico. Unlike in other parts of North America, the men engaged in the work, performed such labor as preparing the fields, planting, and reaping, while the women helped in scattering the grain, weeding, and winnowing. They had no useful domesticated animals, so that the people carried on all the kinds of farm work and the implements were simple, as, the hoe, spade, and basket. They fertilized the soil, let it recover from exhaustion by lying fallow, irrigated by means of canals, surrounded the fields by adobe walls and aloe hedges, and built granaries in which to store the harvests. They mined silver, lead, tin, and copper. Gold was obtained in the form of nuggets on the surface of the ground or from the sand in the beds of rivers. They also got quicksilver, sulphur, alum, ocher, and other minerals which were used in making colors and for other purposes. Although there was an abundance of iron, it was not mined or used. They made tools of copper, hardened with tin. Most of the instruments, however, were of stone, such as axes and hammers. From obsidian, a kind of volcanic glass, by means of pressure they detached long flakes having a razor-like edge, which they used for making knives, razors, lancets, swords, arrow-heads, and spear-heads. They quarried stone from the hills and mountains and often transported large blocks for long distances and erected great buildings.