igoS.] THE PHYSICS OF THE EARTH. 207 



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these plateaus. As the whole region has been raised from the sea by 

 the injection of the land with lava pushed under the crust from be- 

 neath the sea, it is evident that the crust blocks ought to be displaced 

 unequally in different places, and hence the various types of faulting 

 observed. 



It should be remarked, however, that in the elevation of a plateau 

 a mile high, only a layer of lava a mile deep needs to be injected. If 

 three miles high, the layer would have to be three miles thick; 

 but even this maximum height is only about one seventh of the 

 thickness of the crust ; and hence eruptions would not usually occur 

 in these uplifts. The plateaus are all of small height compared to 

 the thickness of the earth's crust, beneath wdiich the movement 

 of molten rock takes place. 



If some faults should thus be widely opened, lava flows of vast 

 extent, like those in Utah and Oregon, might be expected to occur. 

 We cannot give the details of the cracks which produced these gi- 

 gantic outflows, but it is evident that they depended on the opening 

 of immense faults. Now the faults are produced and moved by 

 earthquakes, and earthquakes are due to the leakage of the oceans. 

 It follows therefore that the most immense lava flows ought to take 

 place near the sea ; and this seems to be true both in North America 

 and in Asia, wdiere the outflow in the plateau of Deccan has always 

 excited the wonder of the naturalist. 



That all the faults of the earth's crust depend on the sea and are 

 produced by world-shaking earthquakes, is clearly indicated by the 

 geographical distribution of these cracks in the crust. If any other 

 cause, such as the secular cooling of the globe, were at work, we 

 should find a relatively greater predominance of faults far inland, 

 which is contrary to observation, especially in dry countries. 



It is remarkable that geologists have referred so many phenomena 

 to faulting, hut have made little or no attempt to explain faulting 

 itself. In the present theory referring the origin of faults to the 

 expulsion of lava from under the sea we have for the first time a 

 satisfactory and consistent view of these phenomena. Faults evi- 

 dently arise mainly from the motion of lava in earthquakes, by which 

 the overlying rocks of the crust are broken, and often displaced along 

 the line of fracture. 



