Complex sentence: The area that is now known as Dyker Heights was not developed in the 17th or 18th centuries because the land was too sloped for farming; it remained common woodland until the mid- 19th century.
Split into simpler sentences: The area that is now known as Dyker Heights was not developed in the 17th or 18th centuries because the land was too sloped for farming. It remained common woodland until the mid- 19th century.