From all t.his we see that while water is continually carrying earth 

 and small stones from higher to lower levels and so tending to leave 

 the rocks bare, it is at the same time breaking up the surface of those 

 rocks and so forming fresh soil. If all the soil on a piece of land 

 were scraped off so as to leave the bare rocks exposed, these rocks 

 would in course of time become covered with fresh soil, due to the 

 action of the water that comes down as rain in tearing up the surface 

 of the rocks and reducing the small fragments to fine powder. There 

 is, however, one respect in which this account is very incomplete. 

 Water does not owe its wearing power altogether to its expansion 

 when it freezes. Another property of water greatly assists in this pro- 

 cess, namely, the property it has of taking up certain substances called 

 acids, which are formed chiefly from the decay of plants. These acids 

 are dissolved in the water and greatly assist in its rock-cutting work. 

 To explain the action of these acids would require more space than 

 we can now spare, and so we shall leave it until you come to study the 

 subject of chemistry. We have also said nothing about the small 

 parts of plants that form an important part of all soils. This belongs 

 to botany, and you will readily see the importance of these subjects if 

 you wish to understand fully how soils are made. 



THE UNDEEGEOUND WOEK OF WATEE. 



We now turn to the answer to a question which you must have 

 been inclined to ask some time ago. How do rivers continue to flow 

 when there is very little rain? It is true that in very dry seasons the 

 river contracts a good deal, but it i? clear that it must get supplies of 

 water from somewhere since it continues to flow at all. This leads 

 us to consider the underground work of water. 



The next time there is a heavy shower notice what becomes of the 

 rain that falls on level ground. You will find that where it descends 

 on sand it sinks down as rapidly as it falls, and a short time after the 

 rain is over the surface of the sand will be fairly dry. We have 

 already pointed out that water also sinks through sandstone or lime- 

 stone, though much more slowly, and in a quarry you will probably 

 find that the rock taken out holds a great deal of moisture, which the 

 workmen call "quarry water." But if the rain continues for a long 

 time the pores of these rocks become choked up and no more water 

 soaks in. But see what happens when the rain falls on clay or on a 

 very firm rock like granite. It can not now soak down, for the pores 

 in these materials are much too small to allow the water to pass 

 through rapidly. You will here find it useful to employ two terms to 

 indicate these different actions. Substances which allow water to pass 



