Samuel Bean, a Canadian doctor, had a tombstone erected in Rushes Cemetery near Crosshill, Wellesley Township, Ontario, for his first two wives, Henrietta and Susanna. The original stone was carved in the 1860s and became badly weathered; the following picture shows the more durable replica made to replace it in the 1980s.
What is the message encrypted on the stone, and how can it be decrypted?
Note: the solution is already known, so you could find it by Googling. But it'll be more fun if you manage it by yourself, so no-computers and no cheating! :-)