Hi Tom,
Actually that wouldn't be just a "string" of beads 48 feet long.  Wampum was
usually in the form of a flat, belt-like arrangement, several inches in width,
with intricate purple and white bead patterns worked in.  Also, the beads were
sometimes dyed with various plant-derived pigments, to allow for even more
intricate designs.  Wampum beads here on the east coast were also made from
Busycon whelks.  West coast tribes used strung Dentalium (tusk shells) as
currency, and probably strung Olivella biplicata.  Wampum was originally for
decorative or ceremonial purposes, but came to be used as exchange material
after Europeans arrived on the scene.  In fact, in some of the early American
colonies, wampum came to be used as currency among the European settlers, for
trading with each other, as well as with the native Americans.
Paul M.