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A CORRECTION: G. F. BECKER 
active in this shell, so that the internal heat does not escape to the surface 
solely by conduction and must therefore do work. Nor is it impossible that 
after the final consolidation of the superficial rocks, at from 700° to say 1300°, 
temperature differences of several hundred degrees were set up on equipo- 
tential surfaces. It is a matter of certainty that jointing of the rocks is now 
universal in continental areas and that it has been prevalent from the Archean 
onwards That jointing impedes the flow of heat, thus exaggerating any 
primordial inferiority of diffusivity and tending to increase temperature differ- 
ences, is equally certain. How primeval jointing was initiated is less clear 
than my mistake made it seem to me, and offers an interesting problem. 
GEORGE F. BECKER. 
