Supposed causes of the Elevation of the Land. 213 



astonished to observe how prodigious the weight,— how slender 

 the string that supports it. 



The assigned causes of elevation are exceedingly various. 

 One author raises the bottom of the sea by earthquakes ; an- 

 other, by subterranean fire ; another, by aqueous vapour ; an- 

 other, by the contact of water with the metallic bases of the 

 earths and alkalis. Heim ascribes it to gas; Playfair, to expan- 

 sive force acting from beneath; Necker de Saussure connects 

 it with magnetism ; Wrede, with a slow continuous change in 

 the position of the axis of the earth ; Leslie figured to himself 

 a stratum of concentrated atmospheric air under the ocean, to 

 be applied, I suppose, to the same purpose. 



It is impossible, within the narrow limits of this discourse, 

 that I can enter into the merits of these and other hypotheses 

 seriatim. I must therefore throw them into two classes, the 

 first of explosive forces, the second of sustaining forces ; they 

 are one and the same in Plutonic language, but still it will be 

 convenient to separate them. 



That explosive forces exist, or may exist, under the surface, 

 no one can deny ; but I cannot adopt the opinion (however high 

 the authority from which it comes) that " in volcanic eruptions 

 we find a power competent to raise continents out of the ocean.*" 

 The force we find in volcanic eruptions is hmited in time, place, 

 and action ; it fuses bodies of easy fusibility ; it tosses up those 

 that are refractory, and thus forms either a current of lava 

 or a shower of stones, scoriae, and ashes. What resemblance 

 is there between this operation and the rise of a continent ? 

 With more propriety might it have been said, that in a mole- 

 hill we behold the action of a cause competent to raise moun- 

 tains. 



If by continent is meant a whole continent, and nothing but 

 a continent, its rise, provided this happened only once, would 

 seem difficult to understand ; but to me still more incomprehen- 

 sible is the confident assurance we continually receive from 

 writers of high and deserved reputation, that this event has 

 happened again and again. Before we admit the submersion of 

 a continent, wo must admit either that, at a period immediately 

 preceding that catastrophe, there existed under the land a ca- 

 vity large enough to contain the continent about to be sub- 



