Why are individual states denied the currency power? wikianswers?

the different kinds of money would cause confusion.

Explanation:

Framers gave Congress the power to coin money, meaning the currency power, so there would be an only national monetary system controlled by the federal government.

Section 8 of the Constitution authorizes Congress to coin money and to control its value, whiles section 10 denies that right to the individual states.  

In 1833, since the Second National Bank was shut down by President Andrew Jackson, state banks started issuing their own currencies, which drove to a rush of land speculation that led to the Panic of 1837.