63. What do chemical analyses of river-water prove? Give an example.
What are pot-holes? Give an example of the erosive power of running
water. What amount of mud is carried in suspension by the Mississippi,
and discharged annually into the sea? What estimate has been formed of
the total amount of mineral matter annually transported by that river?
64. What is _alluvium_? How is it formed? and mention some examples of
its occurrence.