NATURE AND FORMATION OF SOILS. 25 



productive soil. On the other hand, the hills, 

 if unprotected by forest (Fig. 8), may be liter- 

 all)' washed away by rain and gully, rivulet and 

 stream, until fertile farms are transformed into 

 sandy wastes. 



Field Exercise No. i . * 



Part i. Work of Atmosphere. — {a) Note any rocks 

 worn away by the friction of rain or sand through the 

 action of wind. Note any rocks kept exposed to other 

 atmospheric agencies through the action of wind ; note 

 an}' wind-blown soil; any wind-blown water; vapor. 



{U) Note any evidences of chemical action; oxidation, 

 hydration, action of carbon dioxide; " rotten rock." 

 Draw a diagram showing successive stages of disinte- 

 gration from solid rock to soil. (This diagram is to 

 represent such a section actually observed in the day's 

 excursion.) 



{c) Note effects of changes of temperature — that is, 

 alternations of heat and cold — upon rocks. 



Part 2. Work of Water. — (a) Note evidences of its 

 solvent power. Fill a small bottle with clear water from 

 a spring or brook, and when you return to the labora- 

 tory evaporate a few drops of it to dryness on a piece 

 of glass or in a test-tube, and see if there is any residue; 

 explain. 



(J)) Disintegrating Power of Water. — Note evidences 



* This outline is meant to be only suggestive of what may be 

 actually seen in a field trip along almost any stream in the 

 north Mississippi valley. Many of the points mentioned will ap- 

 ply to any locality of the United States; some will not. Neither 

 will this outline include (/// that will be found in any excursion. 

 The student will simply omit any points mentioned which he does 

 not actually find, and insert under the proper headings any others 

 found. 



