232 FIRST YEAR COURSE IN GENERAL SCIENCE 



opening. If the rock on either side of the fracture is softer 

 and becomes worn down, the harder rock stands like a ridge 

 or dike. 



EXERCISES . 



1. What changes in the surface of the earth are sometimes caused 

 by earthquakes? 



2. Why is there loss of life by earthquakes when there is no per- 

 manent effect on the earth's surface? 



3. Use the terms cause and effect correctly in describing a connec- 

 tion between volcanoes and earthquakes. 



4. What are the earthquake regions of North America? Of 

 Europe? 



5. What is the volcanic region of North America? Of Europe? 



6. Explain any relation between the answers to Ex. 4 and Ex. 5. 



7. How does one judge whether a volcano is extinct or dormant? 



8. What changes take place in the form of an extinct volcano? 



9. How long have we had any history of California and Oregon, 

 which contain our only volcanoes? 



10. How is volcanic ash made? 



11. Why are volcanoes found in the regions of growing mountains? 



12. Describe a volcanic dike. 



