THE SURFACE OF THE EARTH. 



impression that they must have been once the bottoms of large 

 sheets of water, since nothing but sedimentary deposition could 

 produce a level so uniform. The extent of many of these plains 

 is so great, that in traversing them points may be attained 

 from which all the surrounding country will cease to be visible, 

 so that the prairie presents to the observer a circular horizon, like 

 that witnessed at sea from the deck of a ship. 



As there are, in general, no roads or paths traversing these vast 

 plains, the traveller who ventures across them can only guide his. 

 steps by a compass, or by the stars. 



OUTLINES OF THE LAND. 



104. The prevalence of the peninsular form with the point- 

 ing southwards is one of the most remarkable features in the 

 configuration of the land. The angular point is also generally 

 succeeded or surrounded by one, or several islands ; and where 

 such islands are not apparent, the tendency towards their forma- 

 tion is discoverable by the soundings, which prove the existence 

 of shoals in the places where such islands would otherwise be 

 apparent. A general view of the map of the world will strikingly 

 illustrate these observations. 



10o. The South American Peninsula is an example of such 

 a form upon a grand scale. Like all the other forms of this class, 

 it is a triangle, having its base presented towards the north, and 

 its vertex jutting into the Southern Ocean, where it terminates in 

 the point called Cape Horn. 



Its apex is broken by the ocean into a multitude of islands, 

 the largest of which, separated from the main-land by the Straits 

 of Magellan, is called the Tierra del Fuego, or land of fire, from 

 several volcanic peaks which rise from it to the altitude of 4000 

 feet. The southernmost island of the Fuegian archipelago termi- 

 nates in the headland, or promontory, so well known as Cape 

 Horn. 



106. The North American Peninsula has a like form, its 

 southern point being Mexico ; but instead of terminating in the 

 ocean, it is united with the South American peninsula by a tract 

 of land called Central America, which, taken as a whole, may 

 be regarded as an isthmus, although geographers have, in this 

 case, limited that name to its southernmost and narrowest part, 

 called the Isthmus of Panama. 



107. The "West Indian Archipelago stands in the same rela- 

 tion to the North American peninsula as the Fuegian archipelago 

 to the southern peninsula. This group of islands, celebrated as 

 being the theatre of the great discovery of Columbus, is included 



154 



