VEGETABLE ZONES ON THE PAMPAS. 269 



rapidly gain an ascendancy, and rise to the height of 

 ten or eleven feet. At this time they form an impe- 

 netrable barrier : even the puma and the jaguar 

 cannot push their way amid the strong and prickly 

 stems and leaves, and he who endeavours to pursue 

 his accustomed journey finds himself impeded on 

 every side. Captain Head relates that so speedy 

 is their growth, and so effectual the barrier they 

 present, that an army might be surrounded and 

 imprisoned before it could escape. But as the sun 

 advances in the heavens the tall thistles yield to 

 the increasing heat ; the stems become dry and 

 withered, and are broken down by the hurricanes 

 that sweep over the plains. The nightly dews, also, 

 fall heavy upon them, and occasion a decay as rapid 

 as their first production; thus decomposed, they 

 fertilize the soil, which is again speedily covered 

 with a luxuriant growth of clover : this, in its turn, 

 affords a shelter to the seeds of innumerable thistles, 

 that soon spring up, and cause the prairie's wide 

 extent to appear in the distance like a vast turnip 

 field. 



In these regions wild and wandering tribes occa- 

 sionally pitch their tents at intervals. These are 

 the native Indians, some of whom journey from 

 place to place ; while a few straggling towns and 

 villages, with here and there a solitary hut, betoken 

 the abode of others, who are employed in keeping 

 cattle. They are called Gauchos, and are descended 

 from the Spanish settlers a strong and active race, 

 celebrated for the strength and swiftness of their 

 horses, and their dexterity in noosing wild cattle. 

 Captain Head journeyed with a party of them, during 



