Features of the Earth's Surface. 3538 
greater conductivity would cool more rapidly and therefore con; 
tract more rapidly in a radial direction. These more conductive 
areas, with shorter radii AC, Ac (fig. 
6), would form the sea-bottoms, while 
the less conductive and therefore 
the less radially contracted portions 
B B would become land surfaces. 
would not check the process; for 
Sequent unequal contraction. It seems probable, therefore, 
that the same equality still exists, and that, therefore, the mat- 
ter along the shorter oceanic radi; is denser than along the longer 
Continental radii. If, farther, we suppose great mountain pla- 
teau-masses also to be formed by unequal radial contraction, 
According to Archdeacon Pratt,* the form of the Indian are 
Indicates unmistakably that continental matter and especially 
Himalayan matter is less dense than sub-oceanic matter. i 
view of the origin of the great inequalities of the earth seems 
to be something like what I have presented, since he states his 
belief that the absolute quantity of matter along different radii 
1s the same. T have stated this as a possib/e mode of formation 
of great plateau-masses. As a general fact, however, I account 
or mountain chains in an entirely different manner, which I 
Row proceed to explain. 
* Phil. Mag., vol. xli, p. 307, 1871. 
od 
