156 C. SCHUCHERT THE NORTH AMERICAN GEOSYNCLINES 



^'a very natural and inevitable consequence of the process of subsidence/'' 

 He denied *^the influence of local elevating forces and the intrusion of 

 ancient or plutonic formations beneath the line of mountains, as ordi- 

 narily understood and advocated/' He goes on to say :^ 



"The sinking down of the mass produces a great synclinal axis ; and within 

 this axis, whether on a large or small scale, will be produced numerous smaller 

 synclinal and anticlinal axes. ... I hold, therefore, that it is impossible- 

 to have any subsidence along a certain line of the earth's crust, from the ac- 

 cumulation of sediments, without producing the phenomena which are observed 

 in the Appalachian and other mountain ranges." 



According to Hall, therefore, the internal structure of folded moun- 

 tains was made during the accumulation of the strata in compensation 

 for differential movements of the formations while they were sinking,, 

 and not through lateral thrusting of an eastern inwardly moving land. 

 It further appeared to him that folding had contributed nothing to the- 

 altitude of mountains. Later on, however, the loaded and folded marine- 

 area was subjected to continental elevation in a vertical direction (epeiro- 

 genic), and the elevating was highest in the area of thickest sedimentary 

 accumulation. 



Hall did not say why the continent was vertically elevated, since his 

 views were not a theory of mountain-making, but he held that "mountain 

 ranges were coincident w^th lines of great sedimentary accumulation,"" 

 and that "this accumulation of sediments, with its subsidence and conse- 

 quent folding and plication and the subsequent elevation of the mass and 

 erosion of the anticlinals, had shaped the mountains." Further, "that 

 the mountain elevations were never equal to the vertical thickness of the> 

 strata composing them. I intended to imply that mountain elevation 

 was due to sedimentary accumulation and subsequent continental eleva- 

 tion." « 



DAXA ON GEOSYNCLINES, SYNCLINORIA, AND ANTICLINORIA 



It is apparent from the above that the theory of geosynclines, as we 

 now hold it, had its inception in the idea of trough or syncline areas of 

 sedimentation as set forth in 1857 by Hall. This was, according to Dana,. 

 "the first statement of this grand principle in orography." Then the 

 theory lay more or less dormant until 18T3, when Dana showed^ that the 

 great subsidences of the globe have not been made by the gravity of ac- 



^ Paleontology of New York, vol. 3, 1861, p. 70. 



8 James Hall : Proc. Amer. Assoc, vol. 31, 1883, p. 68. 



9 James D. Dana : On some results of the earth's contraction from cooling, including 

 a discussion of the origin of mountains, and the nature of the earth's interior. Amer. 

 Jour. Sci. (3), vol. 5, pp. 423-443; vol. 6, pp. 6-14, 104-115, 161-172. 



