THE LAND. 285 



during the occurrence of an eruption, small portions of 

 ground have their level permanently altered several feet, and 

 are converted into shelving or flattened eminences, he per- 

 ceives how greatly small accidental variations in the intensity 

 of the subterranean force, and in the resistance which it has 

 to overcome, must modify the form and direction taken by 

 the upheaved particles. In like manner slight disturbances 

 in the equilibrium of the elastic forces in the interior of our 

 planet may have determined their action more towards the 

 northern than the southern hemisphere, and have occasioned 

 the elevation of the dry land in the eastern hemisphere in the 

 form of a wide connected mass, having its major axis almost 

 parallel to the equator, and in the western and more oceanic 

 hemisphere, in a comparatively narrow band, following the 

 direction of the meridian. 



But little can be ascertained by investigation respecting 

 the causal connection of the great phenomena appertaining 

 to the formation of our continents, and to the analogies and 

 contrasts presented by their configuration. We know that 

 a subterranean force was the agent; that the continents 

 were not suddenly formed in their present shape, but that 

 they gradually acquired it by progressive enlargement, or by 

 the junction of smaller masses, effected by a series of 

 successive elevations and depressions, commencing with the 

 siluiian epoch, and continuing to the tertiary. The present 

 form has been produced by two causes which have acted in 

 succession the one after the other : the first is a subterranean 

 reaction, of which the measure and direction are unknown to 

 us ; the second comprises all the causes acting at the surface, 

 as volcanic eruptions, earthquakes, elevations of mountain 

 chains, and oceanic currents. How different would have 

 been the present state of temperature, of vegetation, of agri- 



