198 THE WORLD. 



around us is in a most active state of change, literally speaking 

 there is no such thing as rest. Every operation of nature, how- 

 ever minute and familiar, the heat and the cold, the moisture and 

 the drouth, the warmth of summer and the frosts of winter, the 

 snow and the ice, nay, every drop of rain that falls from the at- 

 mosphere, performs its sharj in displacing and renewing the solid 

 crust of the earth, and contributes its alloted portion in carrying 

 on the great work of universal metamorphosis and change. The 

 great agents of change in the inorganic world may be divided 

 into two classes, the aqueous and the igneous. To the aqueous 

 belong rivers, torrents, springs, currents, and tides ; to the ig- 

 neous volcanoes and earthquakes. Beside these we may enu- 

 merate the agency of the atmosphere, which is partly mechani- 

 cal, and partly chemical; and vital action. We shall consider 

 these several agents of change in order, and see their present 

 effect in changing the sea to land, and land to sea; in excavating 

 valleys and destroying hills ; in the transition of dry ground to 

 marshes, and the reverse ; the occurrence of earthquakes and 

 their phenomena; the uniting of islands with main lands, and 

 insulation of peninsulas. 



In this manner, although we may not be able to comprehend en- 

 tirely the degrading and elevating causes above enumerated, yet 

 we will see abundant means for the conversion of the soil upon 

 which we now tread, from the bed of an ocean to dry land; we 

 shall see how wood has been changed into stone, and plants and 

 fishes imbedded in solid rock. We shall first consider the action 

 of running water. The heated atmosphere which sweeps over 

 the vast ocean and the surface of the earth, absorbs and carries 

 with it an immense amount of aqueous vapor, to be again de- 

 posited when the air is cooled, in the form of clouds, mist or rain, 

 A large amount of this moisture is deposited upon mountains and 

 elevated lands, and thus the more elevated regions become per- 

 petual reservoirs of water, which flows down in gentle streams 

 and rivers, irrigating the plains below. At the first glance we 

 might suppose the amount of water carried up into the air by 

 evaporation was of too trifling a nature to be instrumental in ef- 

 fecting any great mechanical change, but a moments reflection 



