LABORATORY EXERCISES 101 



22. Account for the bubbles that come from a kettle before it 

 begins to boil. What relation has this to water-plants? To fishes? 



23. Which is heavier, sand or clay? Why do farmers call a clay soil 

 "heavy"? 



24. (For classes that have chemistry.) The red and yellow colors 

 of soil are usually due to iron compounds. Ferric compounds cause 

 the red colors; ferrous compounds cause the yellow colors. Why do 

 some red soils have yellow subsoils? Explain the formation of red 

 brick from yellow clay. What would you conclude of the aeration 

 of a soil that has a mottled subsoil? 



LABORATORY EXERCISES 



32. Origin of Soils. 



Field Lesson. If the following points have not been studied in 

 Physical Geography, one or more field trips should be devoted to them : 

 Geological origin of the soils of the region. Evidences of this origin 

 seen in the field trip. Find a rounded pebble; what rounded it? Find 

 a "rotten" stone or a place where a rock is covered by a disintegrat- 

 ing rock; explain. Is the farm land rolling? Account for the low places. 

 What part has the wind played in soil formation? Find some evidence 

 of the work of earthworms, woodchucks, prairie dogs, or other animals 

 in soil formation. Find evidence of the part played by plants in soil for- 

 mation decay of roots, leaves, etc. Cross a meadow or pasture. Are 

 there any spots that are covered with weeds? Are the weeds there chiefly 

 because they kill the grass or because the grass failed to grow? Notice 

 that nature rarely leaves any permanently bare ground. Of what value 

 are weeds in soil formation? If there are any steep hills in the region, 

 notice the relative erosion on hillsides that are forested, tilled, pastured. 

 What use is made of steep hillsides in the neighborhood? Do better 

 crops grow on a hillside or at the foot of the hill? Why? Why are 

 valleys generally fertile? Nearly all of these points that are adapted 

 to the region may be answered in crossing any farm. 



33. Field Lesson. 



Materials. Rule, spade, six fruit-jars. 



Go to a nearby farm. Dig a hole about two feet deep. What is the 

 color of the soil? Of the subsoil? Which is more compact? How deep 

 is the soil? 



Find pieces of partly decayed roots and stems. What color are 

 they? Which contains more of this organic matter, or humus, the soil 



