110 GEOLOGY. 



of rock that icebergs may have dropped there. Captain 

 Couthoy saw one stranded on the Grand Bank, and the 

 water was charged with mud at the distance of a quar- 

 ter of a mile. 



192. Water a great Leveler. By the various ways 

 which I have mentioned, water is continually making 

 additions to the comminuted solids of the earth, the 

 sands, and the soils. This is going on in a large way by 

 the deposit of sediment by large rivers, by the streams 

 at the terminations of glaciers, and by the grindings of 

 icebergs. But much more of this is effected in the ag- 

 gregate by what water is doing in a small way in every 

 part of the earth's surface. The weathering that is done 

 all around you every day is the representative of vast 

 operations that are gradually changing matter in form, 

 locality, and properties over the whole globe. The tend- 

 ency of all this, on the whole, is to bring the heights of 

 the earth down, so that water may be called the great 

 leveler. If there were no operations going on, or to be 

 instituted, in opposition to this tendency, in time the sol- 

 id matter of the earth would be one level, the oceans 

 being filled up with the ruins of the rocks, the water 

 therefore covering up the land, and making a universal 

 ocean. It would require long ages, it is true, to produce 

 this result, but it would finally come. What operations 

 tend to prevent this will be seen farther on. 



193. Agency of Heat. As water generally exerts a 

 leveling influence, heat elevates, and thus tends to pre- 

 serve the equilibrium in the earth's crust. While water 

 wears down rocks, volcanoes are throwing up melted 

 rock to be consolidated as it cools; and earthquakes, 

 which are connected with volcanic action, lift up, as you 

 will soon see, vast tracts of country to a higher level, 

 while the same elevating process is going on in other 

 tracts in a gradual manner. The opposition of the aque- 

 ous and igneous agencies will be more obvious when we 

 come to consider their operation in the construction of 

 the earth in the ages long gone by. 



