THE EARTH AT ITS BEGINNING 



cooling still being pressed very hard at its central parts 

 by the weight of all the gases and liquids round it, till 

 at last the first crust of solid matter began to form on 

 the liquid surface. This crust continued to thicken, 

 but it was subject to many appalling catastrophes and 

 breakages. 



We have already used the occurrence of the tides of 

 the earth as an instance of the Sun's attraction. The Sun 

 (and the Moon) attract the waters of the earth, pulling 

 them up towards themselves. So would they also attract 

 the molten materials of which the early earth was com- 

 posed. The liquid mass would be continually surging 

 like a tide against its wall of solid crust, and the liquid 

 would now and again burst through. There must have 

 been a time when the thin solid crust covering the molten 

 interior became, owing to the solidification and con- 

 traction of the crust, much too small to contain the 

 liquid material. The lava would then break through, 

 and would form huge craters, not unlike some of those 

 which we see on the Moon. We can faintly imagine these 

 terrible outbreaks in which the molten tide rose not 

 thirty or forty feet but many miles high ! 



Later, after some relief had been given by these out- 

 breaks and the crust thickened, the interior regions of the 

 earth by cooling shrank away from the solid shell, which 

 was now too large. This solid shell being insufficiently 

 supported sometimes caved in, and other great outflows 

 of lava resulted. These lava floods dissolved the original 

 solid shell whenever they came in contact with it. The 

 earth probably once had gigantic craters like those which 



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