QUESTIONS. 333 



hydrogen ? State in full what is said of compounds existing in the 

 rocks. What examples are given of incomplete crystalline structure 

 in rocks ? 



69. What is said of the structure of sandstone ? What of rocks 

 composed of a single mineral ? What is a pudding-stone ? What a 

 breccia ? 



70. What is said of stratified and unstratified rocks? Give in full 

 what is said of silicious, argillaceous, and calcareous rocks. How is 

 sulphuric acid used as a test in examining rocks ? 



71. What is the composition of granite? What is syenite? What 

 porphyritic granite ? What is said of the colors of granite ? What 

 is said of its dissemination in the earth ? 



72. What is said of the uses of granite ? What of the presence of 

 pyrites in it ? What of the selection of granite for building ? State 

 in full what is said of gneiss. 



73. What is said of the terms slate, shale, and schist? What of 

 mica schist? Of hornblende slate ? Of talcose slate ? Of clay slate? 

 What is granite rock ? What is said of its varieties ? What of its 

 uses? 



74. State in full what is said about sandstones. What is the mean- 

 ing of the word trap ? 



75. What is greenstone ? What basalt? What trachyte ? What 

 clinkstone ? What is said of the term porphyry ? What of the term 

 amygdaloid ? What form do the trappean rocks tend to assume ? 

 What examples are given of this ? 



76. Describe the ordinary structure of the trappean columns. What 

 is said of the basaltic dike in North Carolina ? 



77. What of Titan's Piazza? State in full what is said of the trap- 

 pean rocks in this country. What is lava ? What are the two classes 

 of lava? 



78. What is scoria? What is pumice? What its uses? What 

 are obsidian and pitchstone ? What is said of the resemblance of 

 lavas to the trappean rocks ? 



CHAPTER IX. 



79. What is said of the substances of which the earth is composed ? 

 If the surface of the earth were not diversified, what would be the ar- 

 rangement of the water and the air ? Give in full what is said of 

 the weight of the earth. What estimates are given of the increase of 

 condensation toward the centre? 



80. Explain what is represented by Fig. 31. 



81. Show how much this figure exaggerates the amount of equato- 

 rial bulging. What influence has this bulging upon the earth's rev- 



