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Show 70 STEPPES AND DESErtTS. World. (Cosmos, vo1. ii. p. 259, and note 405, English ed.) The determination of the ship's place, while Columbus was engaged in traversing the great meadows of sea-weed, is the more important, because we learn from it that for three centuries and a half the situation of this great accumulation of thalassophytes, whether resulting from the local character of the bottom of the sea, or from the direction of the Gulf Stream, bas remained the same. Such evidences of the permanency of great natural phenomena arrest the attention of the physical inquirer with double force, when they present themselves in the ever-moving oceanic element. Although the limits of the fucus banks oscillate considerably, in correspondence with the variations of the strength and direction of the prevailing winds, yet we may still in the middle of the 19th century take the meridian of 41 o W. from Paris (38° 38' W. from Greenwich) as the principal axis of the "great bank." In the vivid imagination of Columbus, the idea of the position of this bank was intimately connected with the great physical line of demarcation, which, according to him, divided the globe into two parts, with the changes of magnetic variation, and with climatic relations. Columbus, when uncertain respecting his longitude (February, 1493), directed himself by the appearance of the first floating streamers of weed (de la primera yerba) on the eastern margin of the great Corvo bank. The physical line of demarcation was, by the powerful influence of the Admiral, converted on the 4th of May, 1493, into a political line, being made the celebrated "line of demarcation" between the Spanish and Portuguese rights of possession. (Compare my Examen Critique, tom. iii. pp. 64-99, and Cosmos, English ed. vol. ii. pp. 279-280.) ( 8 ) p. 27.-" The Nomadic Tt:bbos and Tum·iclcs." These two nations inhabit the Deserts between Bornou, Fezzan, and Lower Egypt. They were first made known to us with some exactness by Hornemam1's and Lyon's travels. The Tibbos or Tibbous roam through the eastern, and the Tuaticks (Tueregs) through the western, parts of the Great Desert. The first are called by the other tribes, from being in continual movement, "birds." The Tuaricks are distinguished into those of Aghadez and those of Tagazi. They are often engaged as conductors of caravans, and in trade. Their |