SUMMARY 439 



What happens to mountains if they are exposed to erosion for a 

 very long time? Where in the United States are such mountains 

 found ? 



What are the causes which produce mountain peaks ? 



How are earthquakes caused ? 



What are the principal industries in mountain regions ? 



How do mountains affect climate ? 



What influence have mountains had upon plants and animals? 



What influence do mountains have upon their human inhabitants ? 



What has been the effect of mountains upon history? 



