284 UNDER THE OPEN SKY 



little of it can crack an iron pipe most of us 

 have found to our cost. And so the water 

 which has percolated through the soil into 

 the rocks freezes there and tears them apart, 

 slowly but completely. 



Thus the rock is split, and the pieces 

 made in this way are again broken into finer 

 and finer fragments until new soil is made 

 to take the place of that which each year 

 moves down to the lowlands. But this new 

 soil lacks fertility. It needs organic matter. 

 So the bacteria act on the old fallen leaves 

 and withered grasses and in the tangle of 

 roots of dead plants, and work them up into 

 the very best of compost for enriching the 

 soil. 



THE SOIL BECOMES POROUS 



These bacteria are as helpless as we are 

 unless they are well supplied with air. On 

 these winter days, as you walk along a coun- 

 try road after a frosty night, you can see how 

 Nature's plowman is at work. Jack Frost 

 is loosening the top layers of the soil and 

 making them porous and airy. Nature 



