Coinman123 is correct that it is a 1730 Spanish silver Real coin... but because you said its diameter "is slightly over one inch" it is the 2 Reales denomination, not an 8 Reales.
In case you don't already know... when the newly-independent United States set up its coinage system, it chose to reject the British system (pounds, crowns, shillings, etc), instead preferring to base the US One Dollar coin on the Spanish silver 8 Reales coin. The 2 Reales coin you found was the basis for the US Quarter-Dollar coin.