Because of the logistical difficulties of dealing with large amounts of money in the form of metals, the Treasury began issuing GoldCertificates and Silver Certificates each redeemable in the respective metal, initially in coin but later in bullion.
This explains the seeming paradox of simultaneous deflation of both Gold and Silver Certificates and coins even as the price of market price of silver declined.
Since the face value of both certificates were the same for the same denomination, as the price gold rose, the ratio of the face value of the Silver Certificate to the market value of silver dropped.