J. L. LOBLEY — THE STUDY OF GEOLOGY. 179 



This unequal distributiou of the land and sea greatly affects the 

 climate of the globe. Had the extent of land been greater, or 

 that of the water less, or, in other words, had the level of the sea 

 been lower than it is, a great part of the earth would have had 

 too low a temperature to allow of the existence of either animal 

 or vegetable life, since the rarefaction of the atmosphere and the 

 cold increase with distance above the level of the sea. 



We thus see what an important part in cosmical economy 

 is played by the vast expanse of ocean, which some may be 

 inclined to think a waste of surface. The climate of the globe 

 would also be seriously modified by a different arrangement of the 

 present extent of land ; for had continents extended from east to 

 west instead of from north towards the south, and had they been 

 massed around the poles, the cold would have been extreme ; and 

 on the other hand, were the continents extended all round the 

 equatorial regions of the globe, leaving the poles as the centres of 

 Tast oceans, the earth would have been uninhabitable by reason 

 of the extreme heat. 



What now is the cause of this beneficial distribution and arrange- 

 ment of land and water ? It is the amount of water on the globe, 

 and the elevation, extent, and direction of mountain chains. The 

 mountain chains of the globe form the skeletons of the land- 

 surfaces, on which all the remainder of the land depends, for did 

 not the great ranges of mountains interpose their barriers, the land 

 would be worn away by the ceaseless action of the ocean's waves 

 and currents, and did not the great chains of mountains supply 

 debris, material would be wanting for the formation of the wide 

 plains which form so large a portion of continental areas. 



We see at once how the size and shape and position of America 

 have been determined by the great range of mountains which ex- 

 tends from the north to the south of that vast continent along its 

 western side, thus protecting it from the destroying action of the 

 Pacific Ocean. On the eastern side of the Andes the land spreads 

 out far to the eastward, permitted by the protection of mountains 

 on the south-eastern coast of Brazil, and by the eastern direction 

 of the currents of the Atlantic on the north-eastern coast. In the 

 northern portion of America, a range of mountains parallel to the 

 Eocky Mountains — the Alleghanies — gives a broad quadrilateral 

 form to North America, with that wondrous valley on which the 

 greatness and the glory of the Great Republic depends, the valley 

 of the Mississippi. In Europe, the Alps, the Dovrefield mountains 

 in Norway, the Apennines in Italy, the Pyrenees and the Sierras 

 of Spain, have each evidently taken part in the determination of 

 the form of the land. In Asia, the Caucasus, the mountains of 

 Syria, and the great central range of the Himalayas, together 

 with the high table-lands of Thibet and Tartary, form the frame- 

 work of the continent. In Africa the relation of the form of the 

 continent to the position and direction of its mountains is, from 

 ordinary maps, less distinctly perceptible. And yet Ave can at once 

 see that Table Mountain has determined the southern termination 



