386 E. C. ANDREW.^ THE HYPOTHESIS OF MOUNTAIN FORMATION 



In the second place, the older mountain systems may be considered as 

 having attained their most spectacular development nearer the conti- 

 nental nuclei than the sites of the greatest ranges of today. The order 

 observed in the geographical distribution of mountains would appear to 

 have been such that the oldest systems of maximum importance were 

 developed in rings progressively nearer the nuclei under consideration in 

 a backward review of time. In other words, there is a great and accumu- 

 lating amount of evidence existing to support the belief that, with the 

 progressive passage of time, mountains extended outward successively in 

 space as rings from the nuclei. 



In the third place, these ancient mountains were arranged in the form 

 of arcs, which are similar in a general way to existing types ; on the other 

 hand, the older members, which have vanished from the landscape, appear 

 to have had a sphere of influence, which extended not so far from the 

 ancient nuclei as the present types, but the individual rings or belts 

 affected were of much greater width than those of present and recent 

 mountains. 



A study of the continents themselves suggests the existence therein of 

 two or more great confocal arcs of crystalline schists which mark the sites 

 of ancient and enormous mountains due to folding. The innermost of 

 these consists of the great continental nuclei themselves, namely, the 

 Scottish Highlands, Scandinavia, Siberia, the Canadian Shield, the 

 Brazilian Shield, the West Australian Shield, peninsular India, and cer- 

 tain parts of Africa. The second occurs beyond the curving belts of the 

 great plains or ^^rairies which separate the nuclei from the outer rings. 

 In America this is indicated bv the belt extendins^ throueii Alaska, the 

 Yukon, British Columbia, Montana, Colorado, Arizona, Texas, and the 

 Appalachians, for Xorth America, and lies beyond the great savannas 

 following the Cordillera from Venezuela to Patagonia, for South 

 America. 



In Australia the second ring is carried through Camooweal from the 

 Northern Territory, through western Queensland, south Australia, 

 Broken Hill, in Xew South Wales, and in all probability a narrow belt in 

 western Tasmania. 



Within Eurasia this second belt appears to follow the Tethyan region, 

 together with the general trend of the eastern coast of Asia. 



The outer l)elt appears to pass, in the case of ISTorth America, from 

 Alaska along the coastal region to southern California, and in South 

 America from Colombia to Patagonia. The trends of North and South 

 America are separated in the Caribbean region by trends that in general 

 are east and west. 



