I think you might be a little confused. Or maybe I'm just misunderstanding you...
Credit is money that is lent out (a debt being incurred to the lender on the part of the borrower), which is not necessarily separate from commodity money. Commodity money does not necessarily imply that people will be carrying around gold and silver in their pockets.
In a free-banking system, most currencies would likely be backed by gold, silver, or perhaps even
agriculture (i.e. grain stores). These widely valued, uniform, easily
measureable and divisible goods can be stored/deposited in warehouses
(a.k.a. banks) for safekeeping, while currencies (a.k.a warehouse
receipts) are used in daily exchanges to represent the actual cash
(gold/silver/grain).
For example, suppose I hold my earnings with Bank X. Bank X issues its
currency to me (receipts), which let's say is representative of a
certain measure of gold that the bank keeps as part of its reserves.
Now, suppose you are a grocer and I buy some apples from you. In order
to pay for my purchase, I give you some Bank X receipts. But suppose
you aren't a customer of Bank X. Suppose you are a customer of Bank Y.
Well, at the end of the day you deposit the Bank X receipts you
received from me in your Bank Y account. Then, Bank Y takes the Bank X
receipts you deposited and redeems them with Bank X for the gold that
they represent. Bank X transfers this gold from its reserves to Bank Y,
and Bank Y deposits the gold in its own reserves.
Translating one bank certificate into another would
not be problematic, as standards of measurement for monies like gold
and silver would likely prove to be the basis for determining currency
values.
The British pound, or "pound sterling," originally got
its name because it was one pound weight of silver. In fact, nearly
every contemporary currency unit originated as a unit of weight of gold
or silver. The U.S. dollar has its own history. In 16th century
Bohemia, a widely circulated and commonly liked one ounce silver coin
was minted in the town of Joachimsthal. They became popularly referred
to as "Joachimsthalers," which was later shortened to "thalers," and
then, of course, "thalers" eventually became "dollars." Upon the U.S.'s
founding, one dollar was the equivalent of 0.8 silver ounces, or 1/20
of a gold ounce.