222 LIGHT SCIENCE FOR LEISURE HOURS. 



that, in speculating on the greater effects which the 

 direct action of rain may once have produced on the 

 surface of certain parts of England, we need not 

 revert to periods when the heat of the climate was 

 tropical.' 



Combining the effects of the sea's action upon the 

 shores of continents, and of the action of rain upon their 

 interior, and remembering that unless the process of 

 demolition were cheeked in some way, each cause would 

 act from year to year with new force one through the 

 effects of the gradual rise of the sea-bed, and the other 

 through the effects of the gradual increase of the 

 surface of ocean exposed to the vaporising action of 

 the sun, which increase would necessarily increase the 

 quantity of rain yearly precipitated on the land we 

 see the justice of the opinion expressed by Sir John 

 Herschel, that, ' had the primeval world been con- 

 structed as it now exists, time enough has elapsed, and 

 force enough directed to that end has been in activity, 

 to have long ago destroyed every vestige of land? 



We see, then, the necessity that exists for the action 

 of some restorative or preservative force sufficient to 

 counteract the effects of the continuous processes of 

 destruction we have indicated above. If we consider, 

 we shall see that the destructive forces owe their effi- 

 ciency to their levelling action, that is, to their influence 

 in reducing the solid part of the earth to the figure of 

 a perfect sphere ; therefore the form of force which is 

 equired to counteract them is one that shall tend to 

 produce irregularities in the surface-contour of the 



