Complex sentence: Apparently named after an owner in the 17 century and probably reclaimed from swamp in the 17th century, by the 18th century it was separated from the main island by a canal roughly following what is now Parnell Place.
Split into simpler sentences: Apparently named after an owner in the 17 century, probably reclaimed from swamp at that time. By the 18th century it was separated from the main island by a canal, roughly following what is now Parnell Place.