220 



ROCKS AND SOIL 



minerals. Rock salt is both a (13)_ 



is a very (15) mineral. It will even (16) 



and a (14) Quartz 



. steel. Rocks 



vary greatly in (17) The brittleness of rock determines in 



large measure how quickly it is changed to (18) In many 



places the beach sand is almost wholly (19) because the 



(20) rock has been ground to a powder. 



STORY TEST 



RALSTON HAS A FINE COLLECTION OF ROCKS AND MINERALS 

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



It has been great fun to make this collection, and I never tire 

 of showing them. First, I'll show you the minerals. This glass- 

 like stone is quartz. It is quite hard but you see I can just scratch 

 it with my knife blade. Here is a white mineral feldspar, easily 

 scratched by quartz. It breaks with more even surface than 

 quartz. See this beautiful specimen of isinglass. I put my 

 knife point under a thin edge and peel off a large transparent sheet. 

 These minerals that I have shown you all came from sedimentary 

 rocks. This piece of marble is an igneous rock because heat helped 

 to form it. Granite is a typical mineral that has been formed by 

 the slow cooling of molten rock; the more slowly it cooled, the 

 larger the crystals in it. Here is a piece of gypsum ; you can 

 scratch it with your thumb nail. This smooth pebble is found in 



the bed of a brook. This 

 chip was probably broken 

 off by ice. The colored 

 streaks in this rock are prob- 

 ably due to the light which 

 reached it while the rest 

 was covered with soil. 



PROBLEM II. WHAT IS 

 THE STORY OF THE 

 FOSSILS ? 



What Are Fossils ? 

 Someone has likened 

 the earth to a book 

 whose pages tell its life 

 story. The leaves of 

 this book are the layers 



A fossil fern-like plant. In what kind of 

 rock would you look for such a fossil? 



