King James Bible Dictionary

a shoal (from the sand drawn thither by the waves) that is the Syrtis Major or great bay on the North coast of Africa

1. Syrtis, the name of two places in the African or Libyan Sea between Carthage and Cyrenaicia, full of shallows and sandbanks, and therefore destructive to ships; the western Syrtis, between the islands Cercina and Meninx (or the promontories of Zeitha and Brachodes), was called Syris minor, the eastern (extending from the promontories of Cephalae on the west to that of Boreum on the east) was called Syris major; this latter must be the one referred to in Acts 27:17, for upon this the ship in which Paul was sailing might easily be cast after leaving Crete