178 J. L. LOBLEY — THE STfDY OF GEOLOGY. 



science will therefore teacli us the formation of continents and 

 oceans, of islands and seas and lakes, of mountain chains and 

 isolated peaks, cones, and hills, of wide-spreading plains, broad 

 valleys, and deep ravines ; of, in short, all those grand features of 

 this beautiful and diversified world which it is the especial province 

 of the geographer to describe. 



But are the land and the sea, though broken up and irregularly 

 divided, equally distributed over the surface of the globe ? On the 

 contrary, the land forms but one-fourth of the whole surface of the 

 globe, and the water or sea three-fourths. Or, to be more accurate, 

 out of the 197 millions of square miles of surface which the globe 

 presents, only about 51 millions of square miles are occupied by 

 the land; the remainder, or about 146 millions of square miles, 

 being covered by the oceans and seas of the world. We thus see 

 how important water is geographically, and we shall subsequently 

 see how important it is geologically. We shall see that water is 

 the great operator on the exterior of the earth ; for water it is, 

 put in motion by gravitation, by winds, by alterations of tempera- 

 ture, or by tidal influence, which has produced that configuration 

 of the Earth's surface which we now see and enjoy. 



The distribution of the land in the northern and southern 

 hemispheres is also very unequal. Of the 51 millions of square 

 miles of land which remain above the waters, three-fourths, it is 

 estimated, are in the northern hemisphere, or north of the equator ; 

 the whole of the dry land in the southern hemisphere not amount- 

 ing to more than about 1 3 millions of square miles. So also, if we 

 divide the globe meridianally into eastern and western hemispheres 

 ])y a meridian running through the Atlantic Ocean, we shall find 

 that much the greater quantity of land lies in the eastern hemi- 

 sphere. Indeed, it is possible to divide the globe into two hemi- 

 spheres in such a manner that nearly the whole of the land may 

 be in one half and nearly the whole of the sea in the other. 



This may be done by making England the centre of one hemi- 

 sphere, and the antipodes of England, or New Zealand, the centre 

 of the other. In the English hemisphere, if I may be allowed to 

 call it so, we shall have the whole of Europe, Africa, and North 

 America, very nearly the whole of Asia, and the greater portion of 

 South America ; while in the antipodal or New Zealand hemisphere 

 we shall find only the southern portion of South America, the 

 East Indian Archipelago, and the Australian and South Sea 

 Islands. Again we shall find that the land is nearly all con- 

 tinental — that is, continuous, and not in detached portions ; for 

 if we exclude the island-continent, Australia, only l-24th of the 

 land consists of islands, all the rest, or 23-24ths-, being continental. 

 Not only is the extent of the surface of the sea much greater in 

 the southern than in the northern hemisphere, but the depth of 

 water is also greater; abyssal depths prevailing in the one and 

 comparatively shallow seas in the other. We see, therefore, that 

 the amount of water is enormously greater in the southern than in 

 the northern hemisphere. 



