46 YIEWS OF NATURE. 



and of the plains of the Arkansas, and therefore, as it were, on 

 the ancient coast chains.* 1 



(7) p. 3-—" When suddenly deserted by the tropical east wind, 

 and the sea is covered with iveeds." 



It is a remarkable phenomenon, although one generally 

 known to mariners, that in the neighbourhood of the African 

 coast, (between the Canaries and the Cape de Verde islands, 

 and more especially between Cape Bojador and the mouth of 

 the Senegal,) a westerly wind often prevails instead of the 

 usual east or trade wind of the tropics. The cause of this 

 phenomenon is to be ascribed to the far-extending desert of 

 Zahara, and arises from the rarefaction, and consequent 

 vertical ascent of the air over the heated sandy surface. To 

 fill up the vacuum thus occasioned, the cool sea-air rushes in, 

 producing a westerly breeze, adverse to vessels sailing to 

 America ; and the mariner, long before he perceives any con- 

 tinent, is made sensible of the effects of its heat-radiating 

 sands. As is well known, a similar cause produces that 

 alternation of sea and land breezes, which prevails at certain 

 hours of the day and night on all sea-coasts. 



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 conjec- 

 tures regarding the extent of Phoenician 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. f " Driven 

 by the east wind," says the pseudo- Aristotle, " Phoenician 



* Humboldt, Relat. liist., t. ii. p. 142, and Long's Expedition to the 

 Rocky Mountains, v. ii. pp. 91 and 405. 



+ Compare S'cyl. Caryand. Peripl., in Hudson, y«q1. ii. p. 53, with 

 Aristot. de Mirab. Auscult. in Op. omnia, ex rec. Bekkeri, p. 884, 

 § 136. , 



