REVIEW OF THE BOOK 295 



which weathering proceeds? Does weathering act on surfaces that 

 are in general level as well as on those that are inclined? Pupils 

 should bring in a stone or brick or some other piece of mineral 

 material that shows the effect of weathering. Why are pebbles 

 rounded? What has become of the particles that have disappeared 

 from them? Why may weathering proceed less slowly on level 

 areas than on steep hills? Why do mountains and hills tend to 

 become rounded? Why are some mountain peaks sharp and 

 others rounded? After weathering has proceeded, how are the 

 detached particles distributed? 



How do plants become agents in the formation of soil? Where 

 do lichens grow? How do roots act in the making of soil? How 

 do animals contribute to the making of soils? What is understood 

 by chemical action (30)? Let the teacher or pupil read some of 

 the extracts from Darwin's book on "Vegetable Mold," explaining 

 how it is that the earth-worm contributes to the formation of soil. 

 Are there any soils in which organic matter predominates; if so, 

 where are they formed, and how? What is humus? How does it 

 modify the texture and color of soils? W T hat is the value of humus 

 (33) ? How may the farmer secure humus for his land? How im- 

 portant do you consider humus to be in the farming of your neigh- 

 borhood? What isamicro-oganism? How do micro-organisms benefit 

 soils or contribute to the growth of plants? Do you understand 

 that the soil is a scene of life as well a collection of materials? 



How is soil transported and laid down? How may stones be 

 a source of benefit to land? What are the chief agencies by means 

 of which soils have been transported? What soils partake most 

 closely of the nature of the bed rock on which they lie? Explain 

 how a stream becomes a transporter of soil. What is muddy 

 water? Let the pupil illustrate what there is in muddy water. 

 What are glaciers? What has been their effect on the soil on a 

 large part of northeastern North America? Determine whether 

 the soils of your region have been modified by the action of 

 glaciers. What influence has the wind in transporting soils? 

 Illustrate from the sand storms of the plains and deserts. Is there 

 (lust in the atmosphere? If so, what is it and how may it be 

 detected? 



