56. What are mineral veins? What is the nature of the quartz veins in granite? How are the minerals usually arranged in the great metalliferous veins? What is a pipe-vein?
57. What are the great geological agents of change?
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.
62. Describe the geological action of rain.
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.
65. How is sediment deposited by a river in a lake?