o9-i E. C. AXDREAVS THE HYrOTHESIS OF MOrXTAIN FORMATION 



gins and western Pacific areas, but also in those regions also of the earth 

 which had come to be regarded as the very symbols of stability, such as 

 peninsular India, Africa, western Australia, the Canadian Shield, the 

 Brazilian Shield, together with the Scandinavian and Siberian nuclei. 

 This is one of the most difficult facts for the student of mountains to 

 explain. 



It is an interesting point to note tliat the mountains of Africa and of 

 India follow the trend of the coasts and have their highest points, or 

 knots, at points corresponding to the large land turns. 



Tliis fact of mountain distribution is most significant, especially when 

 considered in conjunction with the knowledge that these mountains ex- 

 isting today within the old areas of stability are much grander than their 

 predecessors of the early Cenozoic. 



Eelatiox of Yolcaxoes, Earthquakes, axd of igxeous Intrusions 



to mouxtaix formatiox 



earth waves axd yolcaxoes 



The Tethyan group of mountains overlooks sea troughs or deep allu- 

 viated land troughs, whereas the Pacific types on the west overlook the 

 Pacific itself, but on the eastern side they overlook the Pacific in part 

 only; for example, the Coast Range of California. The more inland 

 groups face intermontane valleys. 



Each of these earth waves presents three natural zones : 



First. The outermost arcs are composed either of ocean trenches of 

 remarkable depth or of land troughs partly alluviated. Thus the ocean 

 trenches of the Pacific comprise the H^ckel, Richards, Bartholomew^ 

 Kriimmel, Milne Edwards, Maury, Supan, Tuscarora, Challenger, ISTero,. 

 Pelew, Philippine, Planet, Kermadec, Aldrich, and Tongan deeps, rang- 

 ing from 24,000 to 33,000 feet in depth. The Indo-Gangetio plain, on 

 the other hand, is a magnificent example of an alluviated land trench in 

 the Tethyan area, but being homologous with the Pacific Ocean trenches. 



Second. These mountains, estimated, according to the nature of the 

 case, either from the alluvial plain or the ocean trench, as datum levels 

 present great convex arcs to the ocean or to Tethys. The convexities are 

 connected by appropriate concavities — that is, with mountain arcs whose 

 convexities are directed toward the continental nuclei in the main. Ex- 

 amples of these are the Caribbean or Antillean arcs, the Alps, the Pata- 

 gonian, Falkland, and South Georgian arcs, the Alaskan Knot, the 

 Bolivian Knot, and the Bornean and Celebean arcs. 



Outer arcs in each of these complex rings or earth undulations appear 



