Clarence King — Geologist 



of the earth, he discusses and rejects 

 Hopkins' theory of residual lakes 

 and Mallet's conception of local lakes 

 produced by mechanical crushing. 

 He then advances an hypothesis of 

 his own which may be called that of a 

 critical shell, or couche, 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 temperature 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 treat- 

 ment of this subject : " By the breadth 

 of his treatment and by better and 

 286 



