492 R. T. CHAMBERLIN AND F. P. SHEPARD 



nental borders and coast lines, seems to be an expression of directed 

 horizontal thrusts which are only in part the result of earth shrinkage 

 immediately beneath the mountains. Thus the pressure-box 

 method, with its tangential forces, though not taking into account 

 forces developed by compacting directly beneath the deformed strip, 

 still possesses some advantageous features not possessed by the 

 shrinking rubber-band method. 



The present paper will discuss the bearing of some of the experi- 

 mental results on geological theories. 



ARCUATE TREND LINES 



The remarkable arcuate chains of Asia and southern Europe 

 have given rise to considerable geologic speculation. Suess assumed 

 that in the case of Asia these arcs were produced by thrusting 

 directed from the interior of the continent outward and toward the 

 concave sides of the arcs.' In harmony with this, is the most com- 

 monly held view that, in general, the thrusting which has produced 

 arcuate ranges has been directed against the inner or concave sides 

 of the curves.^ Hobbs, on the other hand, believes that in the for- 

 mation of arcuate mountains, the active thrusting has been directed 

 against the outer or convex side.^ This belief was derived in the 

 first place from theoretical considerations substantiated in his opin- 

 ion by an experiment. In this experiment compressive stress was 

 applied on two sides of what was essentially an equilateral triangle 

 while the apparatus itself offered resistance on the third side.'' The 

 resulting folds naturally tended to form approximately normal to 

 the compression which, in this case, produced an arc whose outer 

 side faced the compression — the result sought. But one may readily 

 suspect that if the thrusting could be made to act in just the opposite 

 direction — from within the triangle outward against the steel sides 



' Eduard Suess, The Face of the Earth, SoUas Trans., Vol. I, Part II. 



^ H. A. Brouwer, "On the Crustal Movements in the Region of the Curving Rows 

 of Islands in the Eastern Part of the East Indian Archipelago," Konig. Akad. Weten- 

 schappen Amsterdam, Vol. XXII (1916), Fig. i, p. 775. O. Wilckens, Allgemeine 

 Gebirgskunde (Jena, 1919), pp. 49-60. 



3 W. H. Hobbs, "Mechanics of Formation of Arcuate Mountains," Jour, of Geol., 

 Vol. XXII (1914), pp. 71-90; 166-88; 193-208. 



" Ibid., Fig. 8, p. 89. 



