If you look very closely at the reverse of this, the sole remaining "class two" 1804 dollar, you will discern a slight shifting of the relationship between the clouds and the lettering above them.
This discrepancy, which distinguishes it from the "class one" and "class three" 1804 dollars, suggests that a new reverse die was employed to strike the coin. This new die was necessary because the old one had either been broken, rusted, or simply discarded after the coinage of 1834, when the class one dollars were struck.
This coin was made a quarter-century later, by a group of enterprising coiners who had decided to go into the rarities business. In addition to making a new die, these midnight coiners had to have stock on which to use it. Instead of following the usual procedure of rolling out a strip of metal to the correct thickness, then blanking it to the correct size-a difficult and expensive process, they decided to start with an existing coin and overstrike it with the new die. That way the new coin would be of about the right weight and thickness. This coin shows traces of the original design: it began its life as a Swiss thaler dated 1857!
When word got out about what was going on, the Mint Director swooped down on the miscreants. All their coins but this one were retrieved and ordered melted down. It remains: a somewhat tarnished, but still legendary rarity.