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 

 riigce. of an envelope now too large for the ball it encloses. He 

 can 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 the 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 



