Applications of the Igneous Theory of the Earth. 91 
the internal surface of the crust. Must not these extensive and 
systematic changes of contact result in the regular development 
_ of the galvanic agent? I propound this question for the conside- 
ration of those who ascribe the polarity of the needle to the regu- 
lar action of electro-magnetic currents. 
I proceed now to the statement of some other physical conse- 
quences of the geological theory, which appear to me to be inter- 
esting in themselves, and which may, by possibility, have some 
bearing on the diurnal and annual irregularities in the declination 
of the needle. 
Modern science has demonstrated that the form of the earth is 
that which would be assumed by a fluid mass of the same mag- 
nitude, and revolving with the same velocity. The surface of 
the ocean at rest and uninfluenced by the heavenly bodies, is a 
continuous portion of the spheroid. Continents and islands are 
portions of the crust which rise above the oceanic surface at every 
variety of elevation within the perpendicular of about five miles. 
There is no good reason to doubt that the submarine valleys de- 
scend below the surface to every degree of depression within a 
still greater perpendicular—greater in the ratio which the oceanic 
surface bears to the continental surface at the same level. 
These irregularities which obtain on the earth’s surface are 
such as the geological theory would lead us to anticipate in con- 
sequence of the gradual contraction of the internal fluid, the oc- 
casional disruption of the primitive crust of the spheroid, and the 
arrangement of the fragments on statical principles. Indeed, the 
geologist must look upon the deep bed of ocean and the emerg- 
ing continent, the mountain range and the river basin, the alter- 
nations of hill and dale resting on strata variously inclined, as the 
ruge@ of an envelope now too large for the ball it encloses. He 
ean hardly fail to perceive, that if the crust were distended to its 
original position by enlarging the volume of the mass within, 
these inequalities would in the main disappear. 
We are not, then, in the light of the geological theory, to con- 
sider the crust of the earth as a continuous, entire and self-sus- 
tained shell ; but as composed of the fragments of the primitive 
envelope of he spheroid, floating on the central fluid, and resting 
against each other at their elevated angles. Continents are the 
result of such a statical disposition of a congeries of larger frag- 
ments ; while minor combinations of masses mutually inclined 
