230 Davis — Framework of the Earth. 



ing as a continuous land mass from middle South 

 America across the then undeveloped Atlantic basin, then 

 widening so as to include all Africa except the folded 

 ranges of its northwestern and far southern borders, 

 and finally crossing the area of the Indian Ocean to the 

 peninsula of India: all this huge element being, like 

 Laurentia and Angara, long undisturbed and having no 

 Mesozoic cover earlier than the Cretaceous overlap. And 

 so on with five other elements of greater or less size and 

 of more or less definite establishment. Let it be noted 

 in passing that it is because of the transverse or dis- 

 cordant attitude of the present Atlantic basin with respect 

 to the remains of the great crustal elements that formerly 

 crossed it, that its border contrasts so strongly with the 

 tangential or sympathetic attitude assumed by the border 

 of the Pacific basin with respect to its limiting elements : 

 this contrast being one of the most striking character- 

 istics of the earth's larger features. 



Next let it be noted that it is especially with regard 

 to the structure and origin of mountain chains that the 

 broad generalizations established by Suess have carried 

 geology so far forward from Lyell's mountainless uni- 

 formitarianism, and so far from de Beaumont's fanciful 

 network of violent upheavals : and also very far beyond 

 various other speculations regarding the origin of moun- 

 tain chains, in which upheavals and compressions were 

 combined in various proportions. For Suess showed that 

 all the greater mountain ranges contradict all theories of 

 axial upheaval and two-sided symmetry, and manifest 

 instead a unilateral structure between a backland or 

 interior area, outward from which the unsymmetrical 

 folding and overthrusting of mountain-making deforma- 

 tion has proceeded, and a relatively rigid foreland or 

 exterior area, towards which the overthrust crust ad- 

 vanced, often with a convex frontal border; while a 

 deeply depressed trough, more or less filled with sedi- 

 ments, is usually found in front of or included within 

 the mountain belt of advancing deformation. But al- 

 though the general structure of mountain ranges thus 

 appears to be correctly worked out, it is highly signifi- 

 cant that neither the unit areas of ancient rocks — Lau- 

 rentia, Angara, Gondwana — nor the mountain ranges 

 that border them can be reduced to any geometrical 

 system. Both the undisturbed areas and the deformed 



