Gresham's Law applied to wampum and gold/silver coins in the 1600s
A key component of Gresham's Law is that people will spend the less valuable asset such as gold or silver if they legally have the same face value.

Sea shells and beads certainly didn't have the same value or demand within the colonies as British coin. You can't pay for import goods, taxes, or use the company store using beads or shells. Instead the issue that the colonies faced was that the British refused to pay them in coin but rather paid them in goods. If your colony wanted the manufactured British textiles then you would send a shipment of tobacco to receive it. There was an extremely limited supply of British coin in the colonies and so as a result alternatives, such as the wampum which was used by the local Indian tribes had to be adopted. 

Eventually the British realized their system wasn't working and began sending over gold and silver coin. These coins were worth more on their face and probably could be considered a less volatile currency and so it was adopted in favor of the wampum which was then phased out of the colonies.