THE BUILDING OF THE EARTH 



exist right through the earth, and which are by no means 

 the same at every place inside the earth, but are, in fact, 

 continually changing, owing to hundreds of causes, the 

 whole of the earth's interior is in a state of unequal 

 strain. What is the consequence that you would expect ? 

 Is it not that the earth should always be making efforts to 

 adjust its weight, and, as it were, to distribute it evenly ? 

 It has been doing this for millions of years. It has not 

 yet finished. 



Lastly, the cover of a golf ball is comparatively a stiff 

 and unyielding substance which does not betray on its 

 surface, if it is allowed to lie at rest, the tensions and 

 strains of the rubber core inside. But the crust of the 

 earth, which we have compared to the golf ball's cover,^is 

 not unyielding or rigid. It is practically a part of the 

 case of the earth ; and it does show and reflect the strains 

 and tensions of the movements and rifts of the core. So 

 that as in the course of ages the straining core changes, 

 and gives way, alters itself and adjusts itself so the 

 crust of the earth alters with it. Some of these changes 

 are sudden and violent. Some of them take place very 

 slowly, occupying thousands or hundreds of thousands of 

 years in the gradual process of change ; and then perhaps 

 for ages the earth's crust will be slowly sinking in one 

 place and slowly rising in another. Thus, what was once 

 a depression in the earth's surface may be now an eleva- 

 tion ; what was once below the level of the sea may 

 be now a continent of land ; and what was once land 

 may now have sunk beneath the incoming sea. Thus, 

 what was sandstone rock of the earth's surface may be- 



27 



