Wampum is the term for the small shell beads sacred to Native Americans. There are two types: white ones made from the inner spiral of whelk shells, and purplish-black ones from the growth-rings of the quahog shell. These are traditionally woven together into belts, the dark beads forming symbolically significant patterns against the white field. Wampum belts are used to commemorate important events, such as the signing of treaties, and are presented ceremonially at marriages. When the European settlers arrived, they quickly realized how vital these belts were to their new countrymen and seized upon them as a trading currency. Wampum were demonetized in the New England colonies in 1663.