Complex sentence: Many soughs were dug throughout the 17th and 18th centuries, until the falling price of lead brought the decline of the Derbyshire lead mining industry towards the end of the 19th century.
Split into simpler sentences: Many soughs were dug throughout the 17th and 18th centuries. The falling price of lead brought the decline of the Derbyshire lead mining industry towards the end of the 19th century.