CHAPTER II. 



LAND AND WATER. 



The Former Condition of the Earth. The earth has not 

 always been as it now is, but has been gradually chang- 

 ing through long periods of years. It is believed that 

 it was once very hot, so hot that all the solid sub- 

 stances now upon it were melted, or converted into gases. 

 As it gradually cooled upon the outside, some of these 

 liquids and gases became solid, and formed a crust upon 

 .the surface. It is believed that the interior of the earth 

 remains to the present day in a very hot condition. 

 There are several indications of this : 



1. In descending into the earth, after passing below 

 the effect of the sun's heat, the temperature becomes 

 higher the farther we descend. 



2. Earthquakes are, in some way, due to movements 

 of the melted substances or gases, or of the crust above 

 them. 



3. Some of the hot liquids and gases are often poured 

 forth from volcanoes. 



It is hardly to be supposed that the whole of the 

 earth's interior is a liquid, because, while the temper- 

 ature may be sufficiently high to melt all known sub- 

 stances, the immense pressure under which all matter is 

 placed at any great depth below the surface must be 

 sufficient to retain it in a solid form, notwithstanding 

 the excessive heat. 

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