456 EMERSON— RECURRENT TETRAHEDRAL DEFORMATIONS. 



Kant-Laplace hypothesis; and the hypothesis of Arrhenius (which 

 was independently deduced by Arldt) of an interior of highly com- 

 primated and heated gas essentially a solid of great density and 

 elasticity, and yet the stupendous movements of the Mediterranean 

 zone and of the Pacific zone of fire in the Miocene seem sufficiently 

 great to meet the demand even of this radical hypothesis. 



With the evidence at hand interpreted in accord with the plani- 

 tesinial hypothesis it is hard to estimate the relative importance of 

 the three great revolutions, the pre-Cambrian, the Permian, and the 

 Pleistocene. It seems probable that they increased in intensity. 

 Would not the tetrahedroid be realized in larger and larger degree 

 as the mass increased and solidified, and be antagonized less quickly 

 and efficiently by the spheroidal tendency as rotation became slower ? 

 Are we not now passing slowly out of an intense glacial period? 



Again would the present equator be so unimportant geologically 

 if it had been with all its tidal strain where it is now, since the early 

 Archaean ? 



The geological map of the earth shows many contrasts and har- 

 monies dependent on this mode of origin. 



Africa is the torpid continent with no border folded mountain 

 chains because it met the average tetrahedral conditions with the 

 minimum of resistance. 



South America and Australia are balanced in relation to the two 

 similar Mediterraneans, each with a large unfolded Archaean area 

 facing Africa and one folded mountain chain farthest from Africa. 

 These chains are, however, of unlike origin and character, the Aus- 

 tralian an outflow chain of the Asian festoon type ; the South Amer- 

 ican a compression chain of the Cordilleran type. This is because 

 the broad abnormally depressed Pacific is the predominant factor 

 acting with compression against South America and with tension 

 from Australia. 



North America is the normal continent, with two bordering 

 mountain chains. In the Permian upfolding the Appalachians 

 flowed west from an elevation east of the present coast, of which 

 there is evidence in the strata, as the beds mainly grow coarser 

 toward the east. The beds flowed west down a virtual slope crum- 

 pling; and curving (stauend) where they met an old land in the 



