PRESIDENT’S ADDRESS—-SECTION C. 93: 
increase or diminution of bulk.” But, if these things are 
probable, it must be possible to frame a hypothesis explaining 
what the changes are and how they are brought about, which is 
not done. 
When we remember that as the earth cooled slowly from a 
gaseous state, the materials composing it must have arranged 
themselves according to their density, it would seem that, after 
a liquid condition had been attained, convection .currents would 
not be possible except on the surface from the poles to the 
equator, and even these would cease as soon as a solid crust was 
formed. Under these circumstances, the deeper parts of the 
earth must be in a state of profound repose with all chemical 
affinities, satisfied for the temperature and pressure, and disturbed 
only by the attraction of the other heavenly bodies. It is then. 
difficult to believe that any chemical reactions on a large scale are 
taking place in the interior masses of the earth, and much more 
difficult is it to suppose that such changes are alternating so as 
sometimes to raise, sometimes to lower, the temperature in the 
same place. At any rate, no one as yet has suggested any 
reasonable explanation of such re-actions, and Dr. Sterry Hunt, 
perhaps our highest authority on this point, says: “ The notion 
of a subterranean combustion or fermentation as a source of heat 
is to be rejected as irrational.” 
Internal Movements.—We have still to consider the hypothesis 
that oscillations of the surface are due to changes in the quantity 
of matter at any particular place brought about by movements of 
a fluid interior. Mr. C. Darwin, in 1838, said that the irruption 
of melted rock into the mountains, which he thought to be a part 
of continental elevation, was caused by some slow but great 
change in the interior of the earth, which, however, he made no 
attempt to explain. Humboldt thought that alterations in the 
molten interior might cause displacements of mass which would 
modify the shape of the earth. Professor J. Phillips, in 1855, also 
thought that the interior of the earth was arranged in con- 
centric layers of different densities, and that intestine movements 
might cause displacements, the less dense portions accumulating 
on some radii, the more dense on others. Those radii with a 
surplus of less dense material would elongate, while those with 
a surplus of more dense would shrink. Very small internal 
changes, he remarks, would alter the length of a terrestrial radius 
by 2000 or 3000 feet. In this way he explained the formation 
of continental and oceanic areas. He thought that an acidic 
magma, being the first to solidify, would segregate under what 
are the continental areas, leaving the more basic lava in still 
liquid lakes, the solid parts having a tendency to rise, the liquid 
tosink. Professor Prestwich said, in 1888, that great continental 
elevations and depressions are ‘due, possibly, to the slow trans- 
ference from one area to another of a partially resisting plastic 
