10 



NATURE AND ORIGIN OF THE SOIL. 



the great piles of rock. We observe that the old rock is weather- 

 ed. If we break off a piece, the fresh surface shows a different ap- 

 pearance from the old weathered surface; it is generally harder. 

 We can rub off some of the old weathered surface; what we rub 

 off is the weathered rock, fine sand or fine clay. We observe long 

 cracks or crevices, some r arrow and fine, some wide and deep. 

 The rains find their way into these cracks and fill them up. Then 

 winter comes on and the water in the cracks freezes. What will 

 happen then? Just what happens when the barrel of rain water 

 freezes, or the down pipes on the house freeze solid, or the bottles 

 of canned fruit in the cellar freeze. There will be a bursting. And 

 even though the quantity of water is small, it must expand, the 

 rocks must give to make room for it. The cracks are made larger, 

 a little of the surface is broken away, or a huge shoulder of the rock 

 is burst off. Gradually, year by year, the rocks are broken up by 

 the frost, the atmosphere wears them away, and the rains wash 

 them down. The rocky cliffs are slowly broken down, and the ice, 

 as it slowly moves down the sides of the mountain, scrapes and 

 scratches off more and more. This material is washed away the 

 larger pieces but a short distance, the smaller pieces further, and 

 the finest sand and clay carried far away, to be dropped or spread 

 out somewhere to make soil. Seeds are dropped by the birds or 

 blown by the winds; some plants sprout, grow, die, and decay and 

 form a little humus. More plants grow and more humus is formed, 

 until out of the material that came from the hard, rough rocks and 

 the decay of roots and leaves a fine soil is formed, sandy in one 

 place, clayey in another, and loamy in another. 





Soil formed from rock underneath. soil with grass growing on it. l> subsoil, coarser 

 and mere rocky. c coarse loose rocks, d rocks in layers, cracked. </ changes to^, c 

 changes to b and b to . 



