MECHANICS QF FORMATION OF ARCUATE MOUNTAINS 8i 



of the Timor arc {d, Fig. 2) by Molengraaff^ has shown a quite 

 remarkable parallel with the Deckenbau of the Alps. Examples 

 of " over thrusting " in extra- Asia tic arcs seem to be augmenting 

 as these are studied with greater thoroughness.^ 



Centrifugal versus centripetal distribution of the active forces 

 which produce mountain arcs. — In a broad way the great Asiatic 

 mountain arcs no doubt 

 owe their location to the 

 presence of lenses of sedi- 

 ments laid down in former 

 epicontinental seas along 

 the borders of the growing 

 continent of Angara. This 

 fact alone would account 

 for their essentially annu- 

 lar arrangement about the 

 ancient coign of the conti- 

 nent as a center. It does 

 not, however, explain the 

 formation of the flexures 

 or the places of location 

 of the individual mountain 

 arcs. There seems to be no 

 difference of opinion that 

 in some way the arcs are 

 due to a system of tangen- 

 tial stresses which operated 

 within the earth's outer 

 shell. Suess has assumed 

 that the system of stresses 



which produced the Asiatic arcs acted from within the arcs out- 

 ward, or, in other words, was centrifugal, the more rigid and 



I Paper read at the Twelfth International Geological Congress in Toronto, 

 August, 1913. 



^See A. Hamberg, "Die schwedische Hochgebirgsfrage und die Haufigkeit der 

 tJberschiebungen," Geol. Rundsch., Ill (1912), 226-35; also Bailey Willis, "Uber- 

 schiebungen in den Vereinigten Staaten von Nordamerika," C.R. IX Cong. Geol. 

 Intern., Wien, 1903 (1904), 531, 539-40. 



Fig. 6. — Outline map of the Asiatic continent 

 and neighboring archipelagoes to show (in black) 

 the seismic zones. Note the close correspond- 

 ence with the outer series of mountain arcs 

 (Fig. 2) and with the zones of volcanoes (after 

 de Montessus de Ballore). 



