Complex sentence: By the early 18th century large salts that were meant to be shared had been mostly superseded by the individual trencher salts, which remained familiar dining accessories through the 19th and into the early 20th century.
Split into simpler sentences: By the early 18th century large salts that were meant to be shared had been mostly superseded by the individual trencher salts. Trencher salts remained familiar dining accessories through the 19th and into the early 20th century.