GLACIERS AND LAKES 253 



8. What is such a change of position (described in Ex. 7) called? 



9. What rate of motion, allowing for no melting, would bring 

 the glacier of Ex. 7 back in 6 months to the position of April 1? 



10. How are long narrow lakes sometimes formed? 



11. Name two other ways in which lakes are made. 



12. How must a lake be situated to furnish, by gravity, a water 

 supply for a city? 



13. Why is the water salt in lakes having no outlet? 



