The Mighty Deep 



heaving upward ; there it is slowly sinking down- 

 ward. True, we do not see or feel such move- 

 ments. But neither do we feel the whirl of our 

 Earth upon her axis, or her rush around the sun. 

 Neither do we see from hour to hour the growing 

 of a boy into a man, or the change from a sapling 

 into a tree. 



Straight through from side to side, the Earth 

 measures some eight thousand miles ; and of 

 those eight thousand a very slight "skin" is all 

 that we can study, by anything approaching to 

 direct observation. No wells or mines on land 

 can be sunk so deep as the sailor's plumbline 

 in the ocean. If we add the six miles or more 

 of the ocean's greater depths to the five miles 

 or more of Earth's higher mountains, we have 

 at most twelve miles, which, compared with the 

 whole diameter of the Earth, must be looked 

 upon as a mere nothing. 



By one means we are able to learn something 

 of what lies deeper in the earth-crust. 



Half a dozen deep wells may be sunk in 

 different places, the same boring apparatus being 

 used, and the same methods being followed. But 

 the same results would not be obtained. Earth's 

 crust is not one solid continuous substance, like 

 a shell of iron. It is made up of different sub- 



112 



