A 1840cc Liberty Seated is counterfeit. Carson City Mint was built in 1869 and struck coins from 1870 to 1893
Regardless of the denomination (dimes, quarters, halves, and dollars ALL used the Seated Liberty design) it would be pretty hard for there to be an 1840CC anything: the Carson City Mint did not begin operation until 1870.If you have a dollar-like coin with that date an mint mark it is almost certainly a counterfeit. The last few decades have seen a flood of fake coins made in the Far East. Some are so good they're almost undetectable as fakes, while many others are laughably bad, with impossible dates and designs. For example, about a year ago I looked at a supposed "rarity" that turned up in California - an 1865 Washington quarter! (correct, 1865). Needless to say, it wasn't even worth the metal it was made from.