The accumulation of sea-weed in the neighbourhood of the western coasts of Africa has been often referred to by ancient writers. The local position of this accumulation is a problem which is intimately connected with the conjectures regarding the extent of Phœnician navigation. The Periplus, which has been ascribed to Scylax of Caryanda, and which, according to the investigations of Niebuhr and Letronne, was very probably compiled in the time of Philip of Macedon, contains a description of a kind of fucus sea, _Mar de Sargasso_, beyond Cerne; but the locality indicated appears to me very different from that assigned to it in the work “_De Mirabilibus Auscultationibus_,” which for a long time, but incorrectly, bore the great name of Aristotle.[AK] “Driven by the east wind,” says the pseudo-Aristotle, “Phœnician mariners came in a four days’ voyage from Gades to a place where the sea was found covered with rushes and sea-weed (θρύον καὶ φῦκος). The sea-weed is uncovered at ebb, and overflowed at flood tide.” Does he not here refer to a shoal lying between the 34th and 36th degrees of latitude? Has a shoal disappeared there in consequence of volcanic revolution? Vobonne refers to rocks north of Madeira.[AL] In Scylax it is stated that “the sea beyond Cerne ceases to be navigable in consequence of its great shallowness, its muddiness, and its sea-grass. The sea-grass lies a span thick, and it is pointed at its upper extremity, so that it pricks.” The sea-weed which is found between Cerne (the Phœnician station for merchant vessels, Gaulea; or, according to Gosselin, the small estuary of Fedallah, on the north-west coast of Mauritania,) and Cape Verde, at the present time by no means forms a great meadow or connected group, “_mare herbidum_,” such as exists on the other side of the Azores. Moreover, in the poetic description of the coast given by Festus Avienus,[AM] in which, as Avienus himself very distinctly acknowledges, he availed himself of the journals of Phœnician ships, the impediments presented by the sea-weed are described with great minuteness; but Avienus places the site of this obstacle much further north, towards Ierne, the Holy Isle. Sic nulla late flabra propellunt ratem, Sic segnis humor æquoris pigri stupet. Adjicit et illud, plurimum inter gurgites Exstare fucum, et sæpe virgulti vice Retinere puppim ... Hæc inter undas multa cæspitem jacet, Eamque late gens Hibemorum colit.