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



tinental plateaux should have varied greatly in their outlines 

 and outer limits, and perhaps thousands of feet in the depth of 

 some portions of the overlying seas, and also that the oceans 

 should have varied in the extent of their lands. The many cha- 

 racteristics of the continental borders — for example, the contrast 

 between the landward and seaward slopes of the mountains and 

 even of the plications constituting them, the positions of volca- 

 noes and of regions of igneous eruptions and metamorphism, 

 indeed all the features declare which side of each border-chain 

 is the oceanic and which the continental, and protest against 

 speculations that would reverse the order. The early defining, 

 even in Archaean time, of the final features of North America, 

 and the conformity to one system visibly marked out in every 

 event through the whole history (in the positions of its outlines 

 and the formations of its rocks, in the character of its oscilla- 

 tions and the courses of the mountains from time to time raised), 

 sustain the statement that the American continent is a regular 

 growth. The same facts also make it evident that the oceanic 

 areas between which the continent lies have been chief among 

 the regions of the earth's crust that have used the pent-up force 

 in the contracting sphere to carry forward the continental de- 

 velopments. 



If this was true of the North- American continent, the same 

 in principle was law for all continents. 



Conclusion. 



I here close this reconsideration of the views brought out in 

 my papers of 1847. Of the principles then presented, and 

 briefly recapitulated in the opening pages of this memoir (No. 303, 

 pp. 42-44, I have found reason to modify some points con- 

 nected with Section 4 (on mountain-making) and part of Section 

 8 (or that on metamorphism) : — the former in consequence of 

 some new considerations of my own and of two ideas, of funda- 

 mental value, which I owe to LeConte*; the other in view of 

 Mallet's recent contribution to Vulcanology. I purposely 

 avoided in my early papers any expression of opinion as to the 

 nature of the earth's interior (having had Hopkins's argument 

 of 1839-1842 in view); and hence there is nothing on this point 

 in the statements then made that requires change f. 



The views on mountain-making now sustained suppose the 



* Introduced in Part I. (No. 303, p. 50) and Part II. (p. 217). 



t The later paper of Professor Hopkins, read before the British Associa- 

 tion, did not appear in this country until after my articles of 1847 were in 

 print ; and 1 have since then been deferring my adoption of the views now 

 accepted from it until the idea of the earth's interior solidity should have 

 additional affirmation from the physical and mathematical side. This it 

 has recently had through the writings of Sir William Thomson and others. 



