igos] THE PHYSICS OF THE EARTH. 203 



on in the depths of the sea, and directly connected with mountain 

 systems spread out on the land. Thus we have shown that the 

 Aleutian Islands are a branch or part of the Rocky Mountains still 

 remaining in the depths of the sea. i\s this part of the chain is now 

 being uplifted by the ocean, we get a very clear conception of how 

 the whole Rocky Mountain system was formed. We are fortunate 

 therefore to find a part of a great mountain chain still unfinished, 

 with one end under water and the main body of the system high 

 and dry along the edge of the continent. 



Now no one believes^ that mountain formation takes place far 

 inland, because the mountains generally follow the coast, and more- 

 over at present the process is found to be most active in the sea, 

 as in the region of the Aleutian Islands and the Antandes. This 

 geographical distribution of mountain-making is therefore a most 

 powerful argument for the new theory. ^Moreover it is generally 

 recognized that the Rocky Mountains in the United States are a 

 good deal older than the Andes in South America ; and as the 

 relative ages bear some relation to the distances from the sea, the 

 mountains on land give the same indication as those still in the 

 depths of the sea. The recession of the sea goes on at very unequal 

 rates in different parts of the world, yet the present positions of the 

 mountains show that the older mountains are generally remote from 

 the ocean. The present theory is therefore confirmed by the lay of 

 the older as well as of the younger mountain systems; and by the 

 situation of the mountains on land as well as of those now being 

 formed in the depths of the sea. All the mountain phenomena of 

 the globe are thus shown to be consistent. But as direct observation 

 of mountain formation witnessed with our own eyes is the most 

 convincing of all evidence, it is fortunate that we are able to cite 

 numerous cases of mountain ranges now developing in the sea. By 

 the study of the sinking going on where trenches are developing, 

 we see how the wrinkles and valleys were produced in mountain 

 systems now at a considerable distance from the ocean. Since the 

 sea recedes from the mountains in the course of geological ages, it 

 follows that more and more land is constantly rising above the water, 



^Compare §42 of this paper, where Leconte's views are quoted at length. 

 He held that mountain ranges are formed on lines of thick sediment along 

 the shores of continents. 



