Wampum consisted of cylindrical beads made from sea shells and was the traditional form of currency used by the great Eastern Woodland tribes of North America. Purple (or sometimes black) beads were produced from the Quahog (North Atlantic hard-shelled clam) and White beads were manufactured from both the Quahog and the North Atlantic Channeled Whelk (a large snail). Owing to their comparative rarity, purple beads had more value than white.
Wampum was kept on strings (hide, sinew, or plant fiber) and was also woven to form elaborate belts. Intricate patterns on these belts were created by alternating the two colors. These patterns consisted of symbols and drawings and could be used to convey stories, record history, or formalize treaties. The symbols are always read from right to left rather than left to right. Individual strings of wampum could serve as a badge of position or authority. Thus, in addition to a its practical use as currency, wampum also had significant cultural, political, and religious value.
Colonists from Europe adopted the use of wampum as currency, especially for trade with the indigenous North American Peoples. This is the origin of the phrase "shelling out" when making a payment and the reason that money is sometimes referred to as "clams" in American slang.