58. What is meant by _weathering_? How are rocks affected at the
surface in tropical countries? What chemical effect has the atmosphere
on calcareous rocks? How is soil formed? How are sand dunes formed?
Mention some effects of the transporting power of the atmosphere.
59. Mention some of the chemical effects of interstitial water. What
is the origin of _travertine_ or _calcareous tufa_?
60. How have _stalactites_ and _stalagmites_ been formed? Give some
instances of the solvent power of springs.
61. How are caves in limestone formed? Describe some of the
appearances of a country composed of calcareous rocks. Describe
briefly how a river erodes its channel.