Prof. 0. Lloyd Morgan—Elevation and Subsidence. 295 
(approximately) spherical crust; and such flattening involves com- 
pression. 
On the view here suggested the earth’s crust, instead of being 
eaten into from below beneath the area of sedimentation, is there 
relatively thickened; while beneath continental areas of denudation, 
instead of being thickened, it is eaten into from below. The occur- 
rence of volcanoes on areas of elevation seems rather to lend support 
to the thinning of the crust in such areas, to its being rent by the 
stress so as to give rise to volcanic fissures, and, as in America, to 
fissure eruptions. Mountains on the Uinta and Park types of flexure 
(Geikie, Text Book,pp. 914-15) are iv accordance with this hypothesis. 
Concerning mountain ranges of the Jura and Alpine type, where 
lateral pressure has come so largely into play, I here say nothing. I 
believe, however, that the principle I am advocating may throw a 
little ray of light on that most difficult subject. 
It may be objected, however, that since liquids transmit pressure 
equally in all directions, there is no reason why the results of that 
pressure should be manifested immediately beneath the loaded area. 
But does not this depend upon the mobility of the liquid? The less 
mobile the liquid, the greater the tendency for the effects of loading 
to be concentrated beneath the loaded area. Beneath an area of 
sedimentation the mobility is much decreased by incipient crystalliza- 
tion. Moreover, we are ignorant how far the liquid substratum is 
continuous, and how far in disconnected reservoirs. ‘The objection 
may be more serious than I imagine. I should be glad of the 
opinion of physicists on this head. 
There is another way in which variations of pressure due to the 
loading and unloading of different areas of the earth’s crust may 
affect the liquid substratum. There can be little doubt that the 
water contained in the magma is above its critical temperature. 
Unless, therefore, it is dissolved in the molten rock, as Mr. O. Fisher 
has suggested, it must be in the state of compressed gas. But such 
a gas would expand and contract under variations of this pressure. 
Even if the temperature be not above the critical point, it must be 
near that point; and the recent researches of Ramsay and Young 
(Phil. Trans. 1886, pt. i. p. 123; 1887 (vol. 178), pp. 57 and 318), 
afford ample confirmation of the fact, first observed in 1835 by 
Thilorier in the case of carbonic anhydride, that near the critical 
point a substance in the liquid state is even more compressible than 
in the gaseous state above that temperature. 
To sum up. If the upper layers are by lateral pressure thrown 
into long geo-clines, there will be from this cause an increased pres- 
sure beneath the geo-synclines, and a diminished pressure beneath 
the geo-anticlines. The pressure on the geo-synclinal area will be 
increased by sedimentation, while that on the geo-anticlinal area 
will be diminished by denudation. This increased pressure beneath 
the area of sedimentation may, it is suggested, squeeze some of the 
underlying magma into a solid state, thus giving rise to contraction 
and further subsidence. It may also cause the further compression 
of the water gas contained in the magma, thus giving rise to further 
