268 SEE— FURTHER RESEARCHES ON [April 24, 



Conclusions. 

 Some of the chief conclusions reached in this and the preceding 

 papers on the physics of the earth may be briefly summarized as 

 follows : 



1. The theory of the secular leakage of the oceans explains satis- 

 factorily six great classes of phenomena, not heretofore closely asso- 

 ciated, namely : (i) Earthquakes, (2) volcanoes, (3) mountain for- 

 mation, (4) the formation of islands, plateaus and continents, (5) 

 seismic sea waves, (6) the feeble attraction of mountains and 

 plateaus long noticed in geodesy. 



2. And the theory not only explains the leading facts of each 

 class of phenomena separately, but also in relation to all the other 

 classes of phenomena ; and this harmonious mutual relationship of 

 all the phenomena proves the theory to rest on a true physical cause. 



3. A vera causa, once established, should not only explain all 

 the phenomena, and all the relations, but also exclude the considera- 

 tion of other possible causes, by necessary and sufficient conditions. 

 This alone ensures the entire validity of the reasoning, and the pres- 

 ent theory meets this severe test perfectly. 



4. We have traced the details of the processes involved in moun- 

 tain formation, and have exhibited illustrations of its working by 

 processes now observed in the depths of the sea. All stages of 

 mountain formation are thus brought out. and they are all shown 

 to be consistent with this simple theory, which explains the princi- 

 pal phenomena of the earth's crust. 



5. This theory explains the distribution of mountains about the 

 continents, their great height which the contraction theory cannot 

 account for; the formation of parallel ridges by the uplift of the 

 side of the trough nearest the sea, when the bottom has so far sub- 

 sided that the folding up of the nearer side becomes the path of 

 least resistance in the expulsion of molten rocks from under the 

 sea. 



6. Several successive troughs are often thus dug out, with ridges 

 forced up between them ; and when the whole is raised above the 

 water we have a series of parallel ranges, such as the Allegheny, 

 Tuscarora and Blue Ridge ]\Iountains in Pennsylvania and Vir- 



