688 T. C. CHAMBERLIN 
6. The distribution of the radioactive substances —If the earth 
were assembled in a fluid state, the radioactive substances should 
have settled toward the center because of their high specific gravity, 
or else, if convection prevented this, they should have been dis- 
tributed sub-equally through the whole mass. There should at 
least have been no concentration of such heavy material in the 
upper layer. But the special investigators of the subject agree that 
if the whole earth were as rich in radioactive substances as its 
accessible portion is, the heat generated would be many times 
greater than the heat now conducted to the surface and radiated 
away. Were this true, the earth should have been growing hotter 
all through its history and no shrinkage at all could be assigned to 
cooling. On the other hand, if the earth were built up of hetero- 
geneous clastic matter that carried its chance portion of radio- 
active particles, and if these, by their heating action, liquefied the 
most susceptible matter immediately enclosing them, and if such 
liquid matter were then squeezed to or toward the surface by the 
powerful extrusive agencies that belong to a solid earth, the radio- 
active substances would be concentrated in the zone of lodgment 
of these igneous portions. ‘This limits the radioactivity to a degree 
that seems to fit the observed facts and the theoretical intimations 
of the case. It is quite obvious that, so far as deformative effects 
assignable to cooling are concerned, the hypothesis of a molten 
earth is seriously embarrassed by this newly discovered source of 
heat superposed on an already embarrassing inheritance of heat from 
its earlier history, while under the hypothesis of a cold-grown 
solid earth, it is a welcome agency. 
The combined import of all the preceding considerations leaves 
the fluid earth embarrassingly short, if not fatally short, of resources 
of energy available for making the observed diastrophic record, 
while the planetesimal earth is much more amply, and apparently 
quite adequately, supplied with such energy, and this becomes 
available in such a slow way as to give great allowances of 
time for the increments of compressive stress to work out their 
adjustments and easements along metamorphic and diastrophic 
lines. 
