EFFECT OF SOLAR INFLUENCES 211 



tlie earth itself. The most important source of energy which 

 is applied to the earth is the heat of the sun. This takes 

 effect on the earth in two diverse ways. In the first place, 

 by warming the water it lifts the vapor of that fluid into the 

 air, whence it is precipitated in the form of rain or snow. 

 In either of these states the part of the precipitated water 

 which falls upon the land moves back toward the sea in the 

 form of rivers or glaciers, bearing with it a share of the 

 earthy or rocky matter with which it comes in contact. This 

 abraded material is in large part deposited next the coast- 

 line ; the principal portion of it, indeed, finds its way to the 

 bottom either within or at the mouth of the natural harbors 

 of our shores. The solar heat also operates in another way, 

 by which it does yet more effective work upon the coast-line. 

 Owing to the differences of temperature which it induces, 

 and the variations in weight of the atmosphere dependent on 

 those variations of heat, the radiation from the sun brings 

 about the movement of the winds. Where these sweep over 

 water surfaces they create waves of a magnitude proportional 

 to the width and somewhat to the depth of the water basin 

 w^iich is traversed, and to the continuity and energy of the 

 air movement. Where these waves roll aeainst the shore 

 they apply the energy which they have received from the 

 wind in rasping the bottom of the shallow water and in 

 beating against the coast-line. 



The two modes of geologic action just adverted to are 

 due to solar heat, and, though widely different in their manner 

 of operation, they have a like origin. The third mode of 

 action which we have to consider is that which arises from 

 the gravitative impulse exercised upon the earth by the nearer 

 and larger celestial bodies, the moon and the sun. While 



