192 INTRODUCTION TO GENERAL SCIENCE 



b. 1201 : 87-91. Limestone and Marble. 



c. 1202 : 123-128. Diatomaceous Earth and the Carbonates. 



d. 1206 : 89-96. Organic Rocks. 



e. 1208 : 28-30. Formation of Limestone, Diatoruaceous 



Earth, etc. 



/. 1209 : 175-183. Geological Work of Marine Animals. 

 g. 1311:76. Limestone. 



h. 1312 : 258. Calcareous and Carbonaceous Rocks. 



Experiment 70. To Test Rocks. 



Apparatus : Medicine dropper. 



Materials: Marble, coral, limestone, unknown rocks, soil, 

 hydrochloric acid, 10 per cent. 



a. Using the medicine dropper, put a drop of acid upon 

 each of the known rocks and note the bubbling or effervescence 

 which indicates the liberation of carbon dioxide. 



6. Test the unknown rocks and the samples of soil. You 

 can recognize the carbonates by this method. 



Imitation coral is a porcelain and cannot be detected by 

 sight or feeling. A drop of hydrochloric acid proves the true 

 coral if bubbles of a gas are produced. 



137. COAL, SOFT AND HARD 



Another variety of organic rock is coal. In prehistoric 

 times plants grew to an enormous size, so that the remains 

 accumulated very fast, and there was a thick layer of decayed 

 vegetable matter on the ground. On account of the great 

 amount of rain, large swamps were formed. Vast layers of 

 this decayed material subsided gradually and were subjected 

 to the high temperature of the interior of the earth and the 

 tremendous pressure, also, of the material on top of them. 

 Under these circumstances, the mass lost its water and gases, 

 and changed to coal. Where the process took place for a 



