THE BUILDING OF THE EARTH 



tion ; ages when it was much lower than it is now, and 

 ages when it was higher. 



We will not at this moment stop to give farther 

 examples. We will only try to see whether there is any 

 explanation which would make it possible to understand 

 why there should be these slow upheavals and subsidences 

 of the earth's surface. The chief and most important 

 reason is that the earth is not so solid as it looks, and 

 not so solid as it feels. It would be easier to realise this 

 if, instead of living in a part of the earth like Great 

 Britain, where there are very few earthquakes, we lived 

 in Japan, or Central America, or in the archipelago of 

 islands which runs from Java to Borneo and further 

 south. In these places, where never a year passes but 

 that the earth can be felt to quiver beneath one's feet, 

 and where earthquakes which wreck houses are at least 

 as common as eclipses of the moon, it is easier to believe 

 that the earth is a rather shaky body ; or, as scientific 

 men would call it, a rather unstable body. But if, like 

 those scientific men who take up the study of earthquakes, 

 or " seismology ," we equipped ourselves with instruments 

 to measure or record earthquakes, we should perceive even 

 in England that the earth is nearly always quivering. 

 Something is always snapping or giving way in its in- 

 terior, and producing trembling fits that sometimes can 

 be felt hundreds of miles away, and sometimes can be felt 

 all over the earth. There are on the average at least 

 twenty earthquakes a year which make the whole of this 

 round globe tremble. 



It would seem, therefore, that either these shocks or 



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