386 Jar/ies on Monticulipora. 
the point of fusion and in so unstable a physical condition that 
the relief of the pressure at any point would cause its instant 
liquefaction. This fact must be borne in mind in all reasonings 
on the problem. 
As the central mass is kept solid by 2Dressure so the superficial 
layers are solidified by cold. They have radiated off into space 
their original heat and being unable on accovmt of the bad con- 
ducting quality of the matter to obtain a sufficient supply to 
replace it from below, they have become as cold as is consistent 
with slow conduction from the heated core and with joowerful 
solar radiation. 
The existence of the viscous layer already mentioned is then 
an almost unavoidable deduction from the history and actual 
condition of the earth. So far as we can judge from the anal- 
ogy of experiments on a small scale the rise of temperature 
downward is much more rapid than the rise of the freezing or 
solidifying-i^oint resulting from increased pressure. It seems 
therefore a necessary inference that at some depth there must 
be a layer where the temperature is so high as to cause semi- 
fluidity in sj^ite of pressure. But the ?-ate of increase of tem- 
perature as above shown becomes less and less until it almost 
disappears. The solidifying effect of pressure therefore, which 
is subject to no such decrease downward, but which rises to the 
very centre at an increasing rate in consequence of greater den- 
sity of the materials, must eventually overtake and surpass the 
liquefying effect of higher temperature and produce solidity in 
spite of the heat. The interval between the levels of supre- 
macy of these two contending forces, heat and pressure, is there- 
fore the viscous layer where neither is supreme. 
(Z'o be continued?) 
MONTICULIPORA, A CORAL AND NOT A POLYZOON. 
BY JOSEPH F. JAMES, M. S., 
Professor of Botany and Geology in Miami University. 
In a late paper upon the " Monticuliporoid corals of the Cin- 
cinnati group," ^ undertaken by Mr. U. P.James and the present 
1 Published in the Journal of the Cincinnati Society of Natural History, 
vols. X and XI. 
