author's views and conclusions 245 



SuEss' Theoky as to Mountain Arcs 



To account for the moiuitain arcs, Suess claimed that the system of 

 ■stresses which produces them has an unbalanced thrust from the rear, 

 and this view has since been quite generally accepted. In his Erin- 

 nermigen, which were published posthumously in 1916, he reveals more 

 clearly than anywhere else that he came to adopt this conception because 

 of the position of the Bohemian "obstruction^^ of granite and gneiss in 

 Europe opposite the vertex of the Alpine and Carpathian arcs, which 

 arcs appeared to him, therefore, to have moved northward at either side 

 where not so "obstructed." Probably also unconsciously the fact that 

 viscous substances flow outward to produce convex borders played some 

 part in fixing this conception in his mind. 



Author's "Views and Conclusions 



, Mountain arcs are, however, very numerous, and such obstructions 

 along their front as the Bohemian mass are altogether exceptional, the 

 only other noteworthy example being that of peninsular India. I have 

 therefore examined the question of the mechanics of arcuate mountain 

 formation and reached the conclusion that the excess of tangential com- 

 pressive stress which is responsible for the evolution of the folded arc 

 has come from the front and below instead of from the rear and above.* 



The Asiatic arcs taken together comprise by far the most perfect illus- 

 tration of the folding process that our planet affords. They represent 

 .a more or less concentric series of compounded arcs which surround the 

 ancient continent of Angara, with each series made up of a number of 

 .arcs linked together. Their study has shown that they have been formed 

 in successive periods, and this not alone on the basis of the strata involved 

 in the folding process, but quite as certainly by the stage of the erosional 

 process which each illustrates. 



It is a generally accepted fact that the effect of close folding is to give 

 to the strata affected additional rigidity, and this should have the effect 

 of causing the area in process of folding to migrate beyond the already 

 formed folds, though such stresses appear to be limited as regards the 

 distance to which they are carried forward within the folded layers. 

 The well-known experiments of Willis on the folding of strata confirm 

 this view. 



The plan of the Asiatic arcs is so extended that it is possible to apply 

 a test to determine what has been the sequence of formation of the 



* Earth features and their meaning, 1912, pp. 437. Mechanics of formation of arcuate 

 mountains. Jour. Geol., vol. 22, 1914, pp. 71-90, 166-188, 193-208, figs. 39. Earth evo- 

 lution and its facial expression. Macmillan, 1921, chapter x. 



