826 



DYNAMICAL GEOLOGY. 



4. EVOLUTION OF THE EARTH'S FUNDAMENTAL FEATURES. 

 The making of mountains involves the making of the earth's fun- 

 damental features. The following are some general considerations 

 bearing on the geographical positions of mountains and their relations 

 to the continental plateaus and oceanic depressions : — 



1. Action of the Pressure against the Continental borders. — The 

 positions of the great mountain-chains along the borders of the con- 

 tinents, and of uplifts, fractures, plications, volcanoes, metamorphism, 

 chiefly on the seaward slope of the chains, prove that, while the force 

 from contraction was a universal force over the sphere, the lateral 

 pressure was vastly more effective in a direction from the ocean than 

 in the reverse direction. Now this landward action of the force seems 

 to be a necessary consequence of the fact that the crust over the 

 oceanic areas was and is abruptly depressed below the level of the 

 continental, so that the lateral pressure from its direction would have 

 had the advantage of leverage beneath the Continental crust, or, 

 rather, would have acted obliquely upward against it. 



In the case of the Appalachians and the other ranges of the Atlantic border, thu 

 mountains front toward the ocean ; that is, have their steepest folds on the oceanic 

 side; and this is a common fact. But the Juras, on the contrary, front inland, toward 

 the Alps, and apparently because of their subordinate relations to the Alps, both geo- 

 graphically and genetically. In each case the}' were on the shoving side; while the 

 greater fractures are usually toward the opposite side. 



2. Pressure against the Continental Borders greatest on the sides of 

 the largest Oceans. — The fact that the largest and loftiest mountain 

 chains, greatest volcanoes, and other results of uplifting and disruptive 

 force, characterize the borders of the largest oceans, shows that the 

 shoving action from the direction of the oceans was approximately pro- 

 portional to the extent of the oceanic basins. 



3. Universality of the Great Movements. — The universality of the 

 great movements resulting from the earth's cooling and contraction is 

 manifested, not only in the relations existing between the continental 

 features and the positions of the oceanic basins, but also in the fact 

 that contemporaneous, parallel movements have taken place in the con- 

 tinents on the opposite sides of the same ocean, and probably in some 

 cases in all continents together. This point is illustrated on page 784. 

 We repeat but one of the facts. The great era of mountain-making, 

 which commenced in the early Tertiary and continued to its end, was 

 a mountain-making era for all continents alike ; in Asia and South 

 America, as well as Europe and North America, mountain ranges 

 were raised over 10,000 feet. 



Again, the mountain ranges made at different times on the same 

 side of a continent have been alike in general direction (p. 796) ; in- 



