744 DYNAMICAL GEOLOGY. 



III. EVOLUTION OF THE EARTH'S FUNDAMENTAL FEATURES. 

 1. Facts to be Explained. 



The principal facts in the earth's system of features, to be explained 

 by the lateral pressure referred to, are the following : — 



1. The continents have mountains along their borders, while the in- 

 terior is in general relatively low ; and these border mountain-regions 

 often include two or more parallel ranges or chains, elevated at differ- 

 ent epochs. 



2. When there are one or more ranges along a border in addition 

 to the main chain, they are almost always situated on the seaward 

 side of the main chain. 



3. The highest mountain-border faces the largest ocean, and con- 

 versely. 



4. The volcanoes of the continental areas are mostly confined to 

 the sea-borders, or the oceanic slope of the border mountain -chains, 

 not because of the vicinity of salt water, but because these were the 

 regions of greatest disturbance and fractures through lateral pressure. 



5. Nearly all of the volcanoes of a continent are on that border 

 which faces the largest ocean : the Pacific is consequently girt with 

 volcanoes. 



6. The strata of the continental borders, especially over the sea- 

 ward slope of the border-chain, are for the most part plicated on a 

 grand scale, while those of the interior are relatively but little dis- 

 turbed. 



7. The folds in the Appalachians and in other border- regions are 

 not usually symmetrical folds, but have one slope much steeper than 

 the other. 



8. The successive changes of level on coasts, even from Archaean 

 time to the Tertiary, have been in general along lines parallel to the 

 border mountain -chains ; as those of the eastern United States, par- 

 allel to the Appalachians, and those of the Pacific side, so far as now 

 appears, parallel to the Rocky Mountains. 



9. The successive mountain-ranges made over the same part of a 

 border-region are generally parallel to one another : e. g., the course 

 of the Triassico- Jurassic uplifts and trap hills is parallel throughout to 

 the Appalachian chain, — the New England part of each having a 

 north-by-east course, and parallel also to the Archaean range of the 

 Adirondacks ; the Pennsylvania part, an east-northeast ; the Virginia 

 and North Carolina part, a northeast. The same general truth is 

 exemplified elsewhere in North America. 



10. The features of the North American continent were to a great 



