the Earth's Contraction from Cooling, 139 



limited in its action to its own side, unless the intermediate 

 stouter region were wholly immovable. 



c. Movements over Oceanic areas. 



The history of the changes of level over the oceanic areas is 

 necessarily a meagre branch of geological science. There are, 

 however, some great truths to be gathered which are of pro- 

 founder import than is generally acknowledged. They show 

 that the oceanic crust has sometimes acted in the capacity of a 

 single area of depression, although of so immense extent. I 

 allude briefly here to only two of the facts, referring the reader 

 to my former articles for a fuller discussion of the subject : — 



First, the remarkable one that nearly all the ranges of islands 

 over the Pacific ocean, and even the longer diameters of the 

 particular islands, lie nearly parallel with the great mountain- 

 ranges of the Pacific coast of North America. There is a dyna- 

 mical announcement in this arrangement — which is partly re- 

 cognized, when we refer it, as I have proposed, to the existence 

 of directions of easiest fracture in the very nature of the infra- 

 Archaean crust, and regard the courses of these feature-lines of 

 the oceans and continents as having reference to one of these 

 directions. But, besides this, there is a declaration with regard 

 to the direction of the pressure that acted against the continents, 

 and reacted over the oceanic areas. 



The other fact is that of the coral-island subsidence, already 

 referred to, which affected the tropical ocean for its whole 

 breadth, or mOre than a quarter of the circumference of the 

 globe — sinking the sea-bottom at least 3000 feet over a large 

 part of the area, and probably over its axial portions two or three 

 times this amount*. The oceanic basin was evidently one basin 

 in its movement ; but the areas of less and greater subsidence, 

 of parallel N.W. by W. trend, so alternate along the southern 

 border of the region of subsidence that we may conclude there 

 were great parallel waves, made by lateral pressure in the crust, 

 as I have elsewhere explained f — that is, geosynclinals and gean- 

 ticlinals, such as are the only possible conditions of the crust 

 under the lateral pressure of the contraction. Now this great 

 oceanic subsidence, involving the breadth of the ocean, if begun 

 in the Tertiary era, as is probable, was going forward at the 

 very time when the Rocky Mountains, and other great moun- 

 tains of the globe, were in progress of elevation, as if these were 

 counterpart movements in the earth's surface ; and it continued 



* Author's Rep. Geol. Wilkes U.S. Expl. Exped. 4to, 1849, p. 399; 

 and < Corals and Coral Islands/ 8vo, 1872, p. 329. 

 t Rep. Geol. Expl. Exped. p. 399 ; * Corals and Coral Islands/ p. 328, 



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