44 Prof. J. D. Dana on some Results of 



mark time for America" (Amer. Journ. Sci., 2nd ser. vol. iii. 

 p. 398, 1847; vol. xxii. p. 346, 1856). 



7. The features of the North- American continent were to a 

 great extent defined in prse- Silurian time, the course of the Azoic, 

 from the Great Lakes to Labrador, being that of the Appala- 

 chians, and various ridges in the Rocky Mountains foreshadow- 

 ings of this great chain, and so on in many lines over the conti- 

 nental surface ; and thus its adult characteristics were as plainly 

 manifested in its beginnings as are those of a vertebrate in a 

 half-developed embryo. 



8. Metamorphism of regions of strata has taken place only 

 during periods of disturbance, or when plication and faults were 

 in progress — allmetamorphic regions being regions of disturbed 

 and generally of plicated rocks. 



The heat required for alteration came up from the earth's 

 liquid interior. (This part of the view requires modification, 

 while the other part, I believe, remains good.) 



9. 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. Volcanoes are indexes of danger, 

 never " safety-valves." 



10. Earthquakes were a result of sudden fracturings and dis- 

 locations proceeding from lateral pressure. In vol. iii. p. 181 

 (1847) occurs the remark ; — "We see that the lateral pressure 

 exerted would be likely to dislocate;" and in the next line, 

 " such fissurings, whether internal or external, would cause sha- 

 kings of the earth [earthquakes) of great violence, and in all 

 periods of the earth's history, and it might be over a hemisphere 

 at once." 



Another important subject (that of the systems in the trends 

 of feature-lines over the globe) is discussed in the articles re- 

 ferred to ; but I pass it by for the present. 



I propose to bring the above principles under consideration 

 with reference to making such changes as may now be necessary. 



I take up, firsts the question as to whether oscillations of 

 level (that is, subsidences and elevations) have been made by 

 the lateral pressure resulting from contraction, as is assumed in 

 my writings on the subject and those of most other authors ; 

 and how was the lateral thrust from the direction of the oceanic 

 areas made to differ in its results from that from the opposite 

 direction ? After which I shall pass to the subjects of meta- 

 morphism, igneous eruptions, volcanoes, the earth's interior, and 

 the origin of oceanic basins. 



