THE HISTORY OF LIFE 163 



the air rain, extremes of cold and heat, the ex- 

 pansion of ice, have kept the mountains continuously 

 in a state of change, a state of decay, disintegration. 

 Thus the rivers carried the disintegrated solid material 

 into the seas, to be deposited ultimately as fine 

 particles on their floors. Vast rivers of ice, always in 

 motion, carried masses of solid matter with them to the 

 commencement of the rivers of water. The waters of 

 the seas and rivers, of lakes and streams, and the water 

 lying in and on the solid earth, were and are con- 

 stantly evaporating to form the gaseous condition 

 of the water molecule. 1 These molecules again con- 

 tracting, aggregate themselves together to form the 

 rain to again destroy mountains and to carry the solid 

 into the streams, the streams into rivers, the rivers 

 to seas or oceans. All an incessant state of change 

 all in perpetual, but often very slow, motion. 

 The solid matter, molecule adhering or cohering to 

 molecule, resists the upheaving pressure from beneath 

 until the strain is overbearing, huge cracks are formed 

 in the layers of the earth, faults causing differences 

 of level of the layers, accompanied by tremors on 

 the earth's surface anon the release from strain is 

 sometimes so violent as to cause the phenomena of 

 earthquakes. Great valleys are cut out by water- 

 courses. Great depressions in the land form the beds 

 of lakes, and presently the confining solid matter gives 

 way, the water rushes from the lake, and a plain 

 between the mountains is formed, and then ultimately 

 man arises and inhabits the fruitful soil. Pressed up 

 hy lateral pressure, we find the layers of earth rising 



1 This process is experimentally shown in " What is Heat ? " 

 p. 287. 



M 2 



