THE SURFACE OF THE EARTH. 



59. Africa. 60. Its cliinatologicul zones. 61. The Tell and 

 Sahara. 62. Valley of the Nile. 63. The central belt. 64. The 

 fourth zone. 65. The southern zone. 66. The coasts. 



1. Origin of the name. The division of general instruction to 

 which the description of the surface of the earth has been con- 

 signed, is called Geography, from two Greek words TT} (ge) the 

 earth, and y^dpv (grapho) I describe. 



2. Preliminary knowledge. The globular form of the earth, 

 its rotation every twenty-four hours on its axis, its poles and 

 equator, the imaginary lines upon it called meridians and parallels, 

 latitudes and longitudes by which the positions of places 

 relatively to the equator and to each other are expressed, the 

 methods of ascertaining these positions for all places, the division 

 of the globe into the northern and southern hemispheres by the 

 equator, and into the eastern and western hemispheres by the 

 meridian of Greenwich, have been severally explained in our 

 Tracts on the " Earth" and on " Latitudes and Longitudes." 

 All these points constitute indispensable preliminaries to any 

 clear or satisfactory knowledge of geography, and we shall there- 

 fore assume in the present Tract that the reader has already 

 become familiar with them. 



3. The distribution of land and water on the surface of 

 the globe forms the first step in geographical knowledge. The 

 entire terrestrial surface measures about two hundred millions of 

 square miles. Very nearly three-fourths of this is covered with 

 water. The whole surface would be so if it were uniformly level. 

 But being unequal, some parts being more elevated, and others 

 less so, the water, in obedience to the law of gravity, settles upon 

 the lower levels, leaving the more elevated parts dry. It is thus 

 that the Almighty has " gathered the waters into one place," and 

 made "the dry land appear," and to the " gathering of waters" 

 has given the name Seas. 



Land is therefore nothing more than the summits and elevutt <l 

 plateaux of vast mountains, the bases of which are at the bottom 

 of the water which thus covers three-fourths of the surface. 



4. The undulations of the terrestrial surface are extremely 

 diversified and irregular, and since the distribution and outlines 

 of the land are determine^ by them, the latter are equally 

 various and complicated. The declivities by which these elevated 

 parts slope downwards, determine the lines according to which the 

 waters of the sea wash them, and these outlines give those 

 peculiar forms and characters to the land, the description and 

 knowledge of which forms a large part of geography. A system 

 of terms has been invented by which these various forms are 

 expressed and classified. 



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