438 FIRST YEAR SCIENCE 



Summary. The high parts of the earth are plateaus 

 and mountains. Some plateaus are dissected by the 

 troughs of rivers that run through them and some are 

 broken by faults. When plateaus are old and worn down 

 they usually show remnants of their former surface in 

 buttes and mesas. 



Mountains are elevations higher than hills. Block 

 mountains are formed by breaks in the rock layers of the 

 earth ; folded mountains are due to folds caused by 

 lateral pressure. Massive mountains are complex in 

 structure and their causes are various. The peaks of 

 mountains are formed by erosion. Many mountains are 

 found in ranges. 



Mountains have a great effect upon climate. The 

 windward side of mountains is usually wet and the lee- 

 ward side dry. The wind, rain, and snow cause ava- 

 lanches, which often do great harm to the plants and 

 animals of the mountains and valleys. 



Mountains have also a great effect upon history. Not 

 only do they form excellent boundaries between nations 

 and states, but they offer protection to weak animals 

 which are unable to withstand their stronger neighbors in 

 the unprotected conditions of the plains. 



QUESTIONS 



Describe the characteristics of a young plateau. 



Why do not dissected plateaus attract a dense population ? 



What are the characteristic features of an old plateau ? 



Where in the United States are broken plateaus found? 



Why are there no lofty old mountains? 



How are block mountains formed ? Where are mountains of this 

 kind found? How are folded mountains formed? Where is a fine 

 example of such mountains to be seen ? 



What are the characteristics of massive mountains? 



