I907.] AND MOUNTAIN FORMATION. 375 



than that of the Aleutian Islands. The latter will eventually connect 

 North America with Asia, and the Arctic will be entirely cut off from 

 the Pacific Ocean. Thus by the study of maps of the ocean depths 

 much light can be thrown upon the past history and present tend- 

 encies of the surface of our globe. Even now we may see the 

 formation of islands, mountains and borders of continents, still 

 going on. Not only is mountain formation and the uplift of islands 

 going on near the margins of the sea, but, also, at considerable dis- 

 tance from the continents, towards the interior of certain oceans. 

 As a good illustration of this interior development we choose the 

 region of the Friendly Islands in the Pacific between Samoa and 

 New Zealand. Here the water is very deep and the narrow trench 

 is built exactly like that near the Aleutian Islands, having on the 

 west a ridge which has been uplifted by the injection of lava from 

 beneath the trough to the east. The Pacific is here developing a 

 long mountain wall on the west, and it will eventually connect 

 Samoa with New Zealand. The earthquakes and seismic sea waves 

 observed in this region show that the process is going on now, and 

 slowly developing a chain of mountains in the open sea, at some 

 distance from any large continent. 



§ 4. On the Development of Islands and Island Chains. — In view 

 of the above considerations, it is clear that small islands are essen- 

 tially mountains under water; and that in the case of large islands 

 the uplifted area was larger, and the bases have since been broadened 

 by the elevation of more land, and the tops flattened by the agencies 

 of wind and water. This was pointed out in the first paper on the 

 cause of earthquakes, §§ 30-38, and attention was called to the lay 

 of the mountains along the centers of the islands, and to the depres- 

 sions in the bed of the ocean near many of them, due to the sinking 

 of the sea bottom, after the crust was undermined in the process 

 of elevation. By a continuation of the process almost any amount 

 of land could be added. When the uplifted area is of considerable 

 extent, the resulting islands are large, and have flat tops, partly 

 owing to the secular effects of such agencies as wind, water and the 

 leveling: action of the waves. Whenever we see a chain of islands 

 in the sea, we know that they are essentially the peaks of a moun- 



