196 



ROCKS AND SOILS 



TOPIC 1. HOW ROCKS WERE FORMED 



SUGGESTED PROBLEMS AND QUESTIONS 



1. What is the age of the earth? 



2. How was our earth formed? 



a. What is the Laplacian hypothesis? 



b. What is the planetesimal hypothesis ? 



3. What is the composition of the earth? 



4. What are the main classes of rocks? 



a. What are igneous rocks? 



b. What are sedimentary rocks? 



c. What are metamorphic rocks? 



5. What are fossils? 



SUGGESTIONS AND HELPS FOR STUDY 



1. Read carefully the problems listed above. Are 

 they questions you have ever wondered about or are 

 now interested in? 



2. The answer to problem 1 is not definitely known. 

 Various estimates of the age of the earth have been 

 made, however. 



3. In connection with problem 5 try to find some 

 fossils in your neighborhood. Look in sedimentary 

 sandstone and limestone. 



4. Problem 4 should be studied with actual speci- 

 mens of sedimentary, igneous, and metamorphic rocks 

 at hand. 



5. Books have been written that will tell you how 

 to identify rocks and minerals. Consult your teacher 

 about them. 



6. In the study of this topic the following words 

 may be new or difficult for you. Study them carefully 

 and use them as often as possible. 



crystalline formed of crystals. 



erode to wear away. 



fossil remains or imprints of plant or animal life in 



rock. 



hypothesis a guess or speculation. 

 sedimentary formed of sediment. 

 soluble able to be dissolved. 

 strata layers of rock. 



EXPERIMENTS OR DEMONSTRATIONS WHICH WILL 

 HELP ANSWER THE PROBLEM QUESTIONS 1 



Activity 124. What kinds of rock are found in the re- 

 gion in which you live? 



Make a collection of all the different kinds of rock that 

 can be found in your community and identify as many as 

 possible. Examine them closely with a magnifying lens. 

 Are they solid in structure or are they made up of separate 



1 See workbook, p. 73. 



grains? Are the grains rounded or angular (with sharp 

 edges) ? Do any of the rocks consist of crystalline grains? 

 Are the grains in layers or scattered? Test the hardness of 

 the rock with the point of a knife blade. Assemble your in- 

 formation in your notebook. 



Activity 125. Where are fossils found? 



Imprints or the remains of plant and animal life in rock 

 are called fossils. Fossils are abundant in limestone, sand- 

 stone, and coal. Explore any quarries in your neighborhood. 

 Examine the rock ledges exposed. What kinds of rock are in 

 them? Do the rocks contain any fossils? Suggest how these 

 plant and animal remains may have come here. 



In your notebook, make drawings of the fossils found. 



OTHER INVESTIGATIONS WHICH YOU CAN MAKE 



1. Explore any quarries that are in your neighborhood. 

 Examine the rock strata that are exposed. 



2. Make a collection of fossils. 



3. Make a collection of all the rocks that can be found 

 in your community and try to identify as many as possible. 

 Closely examine them with a magnifying glass. 



4. Determine the most common type of rock in the re- 

 gion in which you are living. 



5. Visit a museum and examine the rocks, minerals, and 

 fossils that are on exhibition there. 



6. Bring to school pieces of stratified and unstratified 

 rock. 



READINGS WHICH WILL HELP ANSWER THE 

 PROBLEM QUESTIONS 



What is the age of the earth? Man has long won- 

 dered about the size, the shape, the age, and the na- 

 ture of the planet upon which he lives. A study of the 

 literature of primitive peoples shows that their con- 

 ceptions of the earth were limited. The Hindus imag- 

 ined the earth borne by a huge elephant standing on 

 a giant tortoise swimming in a sea of milk. The an- 

 cient Greeks thought the earth ended at the Pillars 

 of Hercules, and they created many legends and 



Courtesy Popular Mechanics Magazine 



FIG. 317. THE NEBULAE HYPOTHESIS 



myths about the relation of the earth to other bodies 

 in the heavens. To those of us who know the facts 

 of the size and shape of our earth these notions of 

 primitive peoples seem highly fanciful and imagina- 

 tive. Yet we should remember that our early ancestors 

 lacked the tools for obtaining an adequate notion of 



