Even though the series was still relatively popular during its final season, it still was canceled as part of the infamous "Rural Purge" when CBS decided to cancel all of their rural and family oriented shows in favor of more edgier programming.
When Sebastian Cabot unexpectedly became ill during the first season, he was replaced by John Williams. It was explained that Giles French was summoned to England by the Queen, and his brother Niles filled in at the Davis' doorstep.