10 TIEWB OF NATURE. 



some occasion deprived these flat regions of their nutrient 

 soil, as well as of the vegetation which it supported. The 

 epoch when this occurred, and the nature of the forces which 

 determined the irruption, are alike shrouded in the obscurity 

 of the past. Perhaps it may have been the result of the 

 great rotatory current (24), which drives the warmer waters 

 of the Gulf of Mexico over the bank of Newfoundland to 

 the old continent, and by which the cocoa-nut of the West 

 Indies and other tropical fruits have been borne to the shores 

 of Ireland and Norway. One branch of this oceanic current, 

 after it leaves the Azores, has still, at the present time, a 

 south-easterly course, striking the low range of the sandy 

 coasts of Africa with a force that is frequently fraught with 

 danger to the mariner. All sea-coasts — but I refer here 

 more particularly to the Peruvian shore between Amotape and 

 Coquimbo — afford evidence of the hundreds, or even thou- 

 sands of years, which must pass before the moving sand 

 can yield a firm basis for the roots of herbaceous plants, 

 in those hot and rainless regions where neither Lecideee nor 

 other lichens can grow (25). 



These considerations suffice to explain why, notwithstand- 

 ing their external similarity of form, the continents of 

 Africa and South America present the most widely differ- 

 ent climatic relations and characters of vegetation. Al- 

 though the South American Steppe is covered with a thin 

 crust of fruitful earth, is periodically refreshed by rains, and 

 adorned with luxuriant herbage, its attractions were not suffi- 

 cient to induce the neighbouring nations to exchange the 

 beautiful mountain valleys of Caracas, the sea-girt districts, 

 and the richly watered plains of the Orinoco, for this treeless 

 and springless desert. Hence on the arrival of the first Euro- 

 pean and African settlers, the Steppe was found to be almost 

 without inhabitants. 



The Llanos are, it is true, adapted for the breeding of cattle, 

 but the primitive inhabitants of the new continent were 



