Applications of the Igneous Theory of the Earth. 93 



the earth's surface. The geological theory suggests the follow- 

 ing solution of the difficulty. The internal expansive agent, 

 finding too tardy a discharge through its ordinary channel, the 

 volcano, expends its force in elevating the fragments of the crust 

 directly over it. The agitation may be confined to the single 

 fragment, or it may be extended to the contiguous group. By 

 way of illustration, we may apply this mode of accounting for 

 these convulsions of nature to the case of the sudden and simul- 

 taneous recession of the waters from the shores of the Sandwich 

 Islands, followed by the return current a few minutes after, oc- 

 curring in 1819, and again in 1837. The supposition of a shght 

 rising and falling of that fragment of the earth's crust on which 

 this group is situated seems to account fully for the phenomena, 

 apparently incapable of explanation on any other hypothesis. 



If the earth's crust is thus fragmentary, it is obvious, that in 

 the gross, it accommodates itself to the form of the internal fused 

 mass on which it rests, namely, the spheroid of revolution. And 

 not only so, but this envelope presents no immovable obstacle to 

 any periodical changes of form which the central fluid may be 

 disposed to undergo. The upper and lower angles of the frag- 

 ments are the joints of the testudo ; and a very slight play of 

 these would be sufficient for all the purposes of accommodation. 



The Newtonian theory of the tides has a very imperfect appli- 

 cation to a superficial fluid like the ocean, of limited depth, and 

 broken by continents and islands. It requires for its perfect ex- 

 emplification a spheroid of revolution fluid to the centre. Pre- 

 cisely such a spheroid is that which the geological theory supposes 

 to be enclosed within the crust of the earth ; and as has been 

 shown, this crust presents no barrier to the action of the sun and 

 moon in accordance with the Newtonian theory. It would seem 

 to be a legitimate conclusion from these premises, that the cen- 

 tral fluid is subject to tides, recurring at any given point twice 

 during each lunar day, a period of about 24h. 50m. ; and it must 

 be further admitted, that there is a constant play of the fragments 

 of the earth's crust, in accommodation to these diurnal changes 

 of form in the central fluid. 



Can we have proceeded thus far in our speculations, without 

 being prepared to admit that the oceanic tides, instead of being 

 the direct result of the action of the sun and moon, in accordance 

 with the Newtonian theory, are but a secondary efiect — ^in part 



