EFFECTS OF THE MOVEMENTS OF WATER 39 



In many other regions of the world, even in regions now 

 tropical, we find evidence that once there were glaciers. 



FIG. 17. Glacial scratches. After SALISBURY. 



QUESTIONS 



1. Why did people once prefer to live near rivers? 



2. What is erosion? 



3. Why is not the whole surface of the land worn down nearly 



to sea-level? 



4. What is a "drowned valley"? 



5. How do we know that some rocks were formed in the sea? 



6. What becomes of the rain that falls on the earth? 



7. Why is "ground- water" important? 



8. What is the water-table? 



9. In what layers of soil does the ground-water move? 



10. Explain an artesian well. 



11. What is a glacier, and what does it do to the surface of the 



earth? 



