THE STORY OF NINETEENTH-CENTURY SCIENCE 



changes. The solidest rocks are day by day disinte- 

 grated, slowly, but none the less surely, by wind and 

 rain and frost, by mechanical attrition and chemical 

 decomposition, to form the pulverized earth and clay. 

 This soil is being swept away by perennial showers, and 

 carried off to the oceans. The oceans themselves beat 

 on their shores, and eat insidiously into the structure of 

 sands and rocks. Everywhere, slowly but surely, the 

 surface of the land is being worn away; its substance is 

 being carried to burial in the seas. 



Should this denudation continue long enough, thinks 

 Hutton, the entire surface of the continents must be 

 worn away. Should it be continued long enough! And 

 with that thought there flashes on his mind an inspiring 

 conception the idea that solar time is long, indefinitely 

 long. That seems a simple enough thought almost a 

 truism to the nineteenth-century mind ; but it required 

 genius to conceive it in the eighteenth. Plutton pon- 

 dered it, grasped its full import, and made it the basis of 

 his hypothesis, his " theory of the eartlv' 



The hypothesis is this that the observed changes 

 of the surface the earth, continued through indefinite 

 lapses of time, must result in conveying all the land at 

 last to the sea; in wearing continents away till the 

 oceans overflo\v them. What then ? Whv, as the con- 

 tinents wear down, the oceans are filling up. Along 

 their bottoms the detritus of wasted continents is de- 

 posited in strata, together with the bodies of marine 

 animals and vegetables. Why might not this debris 

 solidify to form layers of rocks the basis of new con- 

 tinents ? Why not, indeed ? 



But have we any proof that such formation of rocks 

 in an ocean-bed has, in fact, occurred ? To be sure we 



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