Gravesend

 was a shore area near London.

The shore was separated from the water by marshes with pockets of quicksand.

Captain Sal Winter ran her ship, the Demeter, aground in the Gravesend marshes while being pursued by Captain Stanislaus on the Teazer. She fought Stanislaus and was killed by Prince Rupert. Ben Jackson, who was travelling with her, got almost swallowed by quicksand trying to get to the shore, but was saved by Nathaniel Scrope. (PROSE: The Roundheads)