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



1. The defining of the continental and oceanic areas began 

 with the commencement of the earth's solidification at surface, 

 as proved by the system of progress afterward. 



2. The continental areas are the areas of least contraction, 

 and the oceanic basins those of greatest, the former having 

 earliest had a solid crust. After the continental part was thus 

 stiffened and rendered comparatively unyielding, the oceanic 

 part went on cooling, solidifying, and contracting throughout ; 

 consequently it became depressed, with the sides of the depres- 

 sion somewhat abrupt. The formation of the oceanic basins and 

 continental areas was thus due to " unequal radial contraction "*. 



3. The principal mountain-chains are portions of the earth's 

 crust which have been pushed up, and often crumpled or pli- 

 cated, by the lateral pressure resulting from the earth's con- 

 traction. 



4. (a) Owing to the lateral pressure f from contraction over 



of Prevost's papers on the origin of mountains had been published six years 

 before, but I knew nothing of his views until after my paper was ready for 

 publication, as I remark in a paragraph near its close. 



* The principle thus expressed by Professor LeConte in volume iv. of 

 the same journal (1872) does not differ essentially from my old view, ex- 

 cept that it is connected with the idea of a solid globe. Professor LeConte, 

 on p. 466 of his article, attributes to me the opinion that the " sinking of 

 sea-bottoms, determined by interior contraction, is the [source of the] force 

 by which continents are elevated.'* 5 But I have never referred the origin 

 of continents to such a cause, or to any other than that stated above. 



Moreover the elevation of mountains on the borders of continents I have 

 attributed, not to " sinking sea-bottoms " merely, but to lateral pressure 

 produced by contraction over continental as well as oceanic areas, that on 

 the oceanic being made much the greatest, as stated beyond. My language 

 is frequently ambiguous on this last point, because I speak of the oceanic 

 as the " subsiding' 1 areas. But the term is used relatively. In volume iii. 

 on p. 17^ (1847) I observe that mountain elevations occur "near the limit 

 between the great contracting and the non-contracting (comparatively non- 

 contracting) areas;" and in various places I describe the contraction as 

 general. In my ' Manual of Geology/ on page 732, I remark that the 

 elevating " force acted most strongly from the oceanic direction," which 

 was the idea throughout. I do not deny, however, that I have supposed 

 too large a part of the lateral force to have come from the special contrac- 

 tion and consequent subsidence of the oceanic part of the globe. 



Professor N. S. Shaler, in 1866 (Proc. Boston N. H. Soc. vol. x. p. 237, 

 vol. xi. p. 8, and Geol. Mag. vol. v. p. 511), presented, as original, the idea 

 that " mountain-chains are only folds of the outer portion of the crust caused 

 by the contraction of the lower regions of the outer shell," and that "the 

 subsidence of ocean-floors would, by producing fractions and dislocations 

 along shore-lines, tend to originate mountain-chains along sea-borders and 

 approximately parallel to them," which is essentially the view that LeConte 

 attributes to me. These ideas are coupled with others respecting limita- 

 tions of the action of contraction due to denudation and deposition, in 

 which I have no share. 



t In my papers in 1847 I used the terms lateral pressure, lateral force. 



