236 ROCKS AND SOIL 



of the earth are heated by subterranean (19) beds. These 



waters bring mineral matter to the surface in boiling (20) and 



(21) (22) soil is that which remains in the place where 



it was produced. Soil moved to other localities by moving ice or 

 water is called a (23) soil. 



STORY TEST 



AN EXTRACT FROM ANNETTE'S NOTEBOOK ON SOILS 

 Read carefully and critically. List all the errors and suggest corrections. 



Soil has not always existed on the earth ; it is therefore not an 

 essential factor of our environment. Before soil was formed, the 

 solid part of the earth was entirely sedimentary rock. Rocks 

 decay, crumble, and are reduced to soil through the agencies of 

 weathering but also through mechanical action of wind, water, 

 and ice. Perhaps you have seen how granite steps wear away 

 more quickly than marble steps. Our finest buildings quite often 

 have marble floors because of their durability. When water 

 contains nitrogen from the air in solution, it will dissolve limestone 

 and marble. Much soil in northern United States is transported 

 soil brought by running water and ice. Rocks on mountains are 

 more exposed than elsewhere, and for that reason the soil is deeper 

 on mountains than in valleys. Many rocks are eroded just by 

 the action of the oxygen of the air combining with the iron in the 

 rocks. There is still heat in the interior of the earth and in some 

 places underground water is made to boil, causing hot springs and 

 geysers. These waters have nothing to do with soil formation, 

 however ; the water may spout out and flow back, or it may flow 

 continually as in any cold-water spring. 



PROBLEM IV. WHAT SOILS ARE BEST FOR 

 AGRICULTURE ? 



Differences in Soils. We have seen that soil is weathered 

 rock, that either remains in place, or is carried away by 

 erosion. When water transports soil, it tends to sort out 

 and distribute different-sized particles to different places. 

 But if the volume and speed of the water change, a layer 

 of fine material may be placed upon a layer of coarse 

 material, or a fine-grained sediment may be laid upon a 



