86 THE NEW AGRICULTURE. 



clay soils are wet because they retain the water, and prevent it 

 from freely descending into the earth. 



" The rocks beneath besides being in many cases porous in their 

 texture, such as sandstone, are all more or less traversed with 

 cracks; sometimes mere lines, like those of a cracked windoAv-pane, 

 but sometimes wide and open clefts and tunnels. These numerous 

 channels serve as passages for the underground water. Hence, al- 

 though a rock may be so hard and close-grained that water does 

 not soak through it, yet if that rock is plentifully supplied with 

 these cracks it may allow a large quantity of water to pass through. 

 Limestone, for example, is a very hard rock, through the grains of 

 which water can make but little way; yet it is so full of cracks or 

 " joints," as they are called, and these joints are often so wide, that 

 they give passage to a great deal of water. 



" In hilly districts, where the surface of the ground has not been 

 brought under the plow, you will notice that many places are 

 .marshy and wet, even when the weather has been long dry. The 

 soil everywhere around has been perhaps baked quite hard by the 

 sun; but these places remain still wet, in spite of the heat. Whence 

 do they get their water ? Plainly not directly from the air, since 

 in that case the rest of the ground would also be damp. They get 

 it not from above, but from below. It is oozing out of the ground; 

 and it is this constant outcome of water from below, which keeps 

 the ground wet and marshy. In other places you will observe that 

 the water does not merely soak through the ground, but gives rise 

 to a little run of clear water. If you follow such a run up to its 

 source, you will see that it comes gushing out of the ground as a 

 spring. 



"Springs are the natural outlets for the underground waters. 

 But, you ask, why should this water have any outlets, and what 

 makes it rise to the surface ? Let us suppose that a flat layer of 



