NATIONAL ACADEMY OF SCIENCES. 



Again, in endeavoring to account for the formation of those 

 types of granite that pass into gneiss and crystalline schists of 

 essentially the same chemical composition, hut which show no 

 evidence of having been subjected to such excessive heat as would 

 produce actual liquefaction, he called in the agency of the im- 

 mense pressure to which such rocks would necessarily have been 

 subjected. While the long years of combined field work and 

 microscopic study of modern petrographers, made since King's 

 theory was enunciated, have proved that the structure of crystal- 

 line schists is due to pressure, they do not go so far as he did in 

 assuming that the end product of such mechanical pressure might 

 be granite. 



Perhaps his most enduring theoretical discussion of that time 

 was that on hypogeal fusion, in which, accepting the validity 

 of the physical arguments against the fluid interior of the eartli, 

 he discusses and rejects Hopkins' theor}^ of residual lakes and 

 Mallett's conception of local lakes produced by mechanical crush- 

 ing. He then advances an b^othesis of his own which may be 

 called that of a critical shell, or couclie, between the permanently 

 solid interior and the outer crust of the earth, which is above the 

 temperature of fusion but restrained from fusion by pressure. 

 In this, therefore, the opposing forces of pressure and tempera- 

 ture hold themselves reciprocally in equilibrium, but when this 

 equilibrium is disturbed, as, for instance, by a sudden change of 

 the relative position of isobars and isotherms— say by local 

 erosion and rapid transfer of load within limited areas— local 

 lakes of fusion would be created. Iddings, in his "Origin of 

 Igneous Rocks," says of King's treatment of this subject : "By 

 the breadth of his treatment and by better and fuller data he 

 advanced the problem of the origin of the various kinds of vol- 

 canic rocks far beyond the point reached by any of his prede- 

 cessors." 



In his chapter on Orograplry, King says, in speaking of the 

 causes of crust motion: "I can plainly see that were the critical 

 shell established its reactions might thread the tangled maze of 

 phenomena successfully, but I prefer to build no farther until 

 the underlying physics are worked out." He was at that time 

 already very strongly impressed with the imperfection of the 

 then existing knowledge of terrestrial thermodynamics and the 



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