Part 10

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?

66. What is the difference between lacustrine and fluvio-marine deposits? What is a delta?

67. Describe the geological action of frost. Describe the geological action of river-ice.

68. What are glaciers? What thickness do they attain in the Alps? What is their rate of motion? What are crevasses, and how do they originate? What are superficial moraines? What are terminal moraines? What changes does a glacier effect upon its bed, and how are these modifications produced? What is the character of a glacial river? What is the origin of icebergs? How is the general absence of blocks and stones in Greenland icebergs to be explained? What is the nature of a submarine terminal moraine? What is the ice-foot? What is the chief agent in distributing erratic stones and blocks over the sea-bottom? What effect upon the sea-bed must stranding icebergs produce?

69. What are some of the chemical compounds held in solution in sea-water? Which of these go to form the shells and skeletons of marine animals?

70. Describe the action of breakers on a sea-coast. How does frost aid the wasting action of breakers? What effect has the nature of the rocks in the production of inequalities in a coast-line? Upon what part of the sea-bottom does the material derived by the action of the breakers chiefly accumulate? What effect have the tides and ocean currents in the distribution of sediment?

71. What is the general rule as regards fine-grained and coarse-grained deposits? Mention a partial exception to this rule. What effect have tidal currents in shallow seas?

72. How are rocks disintegrated through the action of plants? What is peat? What may be inferred from the occurrence of shell-marl underneath peat? What does the appearance of roots and trunks of trees, and of remains of land animals under peat, indicate?

73. What, generally, is the geological action of animal life?

74. What is coral? What is a fringing reef? What is the general character of a barrier reef? Give an example of one. What is an atoll? What is the nature of coral rock? What is Mr Darwin's theory of the formation of coral reefs?

75. What is the nature of the Atlantic ooze? In what respects may it eventually come to resemble chalk and limestone? Mention an instance of the abundant occurrence in the sea of animalcules with siliceous coverings and skeletons. What is the nature of the red clay found at great depths in the Atlantic and Southern Oceans?

76. What are some of the notions held in regard to the internal condition of the earth? At what (average) rate does the temperature of the earth's crust increase as we descend from the surface?

77. What is the nature of the movements to which the earth's crust is subjected?

78. Describe the hypotheses advanced to account for earthquakes. Mention some of the effects of earthquakes--1st, as regards alterations of level; and 2d, as regards modifications of the surface.

79. Mention a good example of tranquil elevation and depression of the earth's crust. Mention some of the proofs of an elevatory movement. Give proofs that shew depression of the land. How may certain former changes of sea-level be accounted for without inferring any movement of the land?

80. What effect must depression have upon the strata forming the earth's crust? What is the result of a movement of elevation? What is the cause of cleavage?

81. What is the nature of the materials thrown out during volcanic eruptions? What is the general structure of a volcanic cone? How does molten rock make its escape from the orifice of eruption? What is the meaning of the terms lapillo, puzzolana, and ceneri?

82. What is lava? Describe the general appearance and mode of progression of a stream of lava. What effect is produced upon fragments of rock caught up and inclosed in lava; and what changes are caused in the pavement upon which it cools? How does a lava stream entering a lake or the sea behave in regard to the sediment gathering therein? To what is the basaltic structure due? How are the axes of the prisms in a columnar igneous rock arranged? Name some of the varieties of lava. What is the origin of the vesicular structure in igneous rocks? What portions of a bed of lava are most frequently scoriaceous? In what kinds of lava is the vesicular structure most abundantly met with? How have the vesicles become flattened? In what manner have they been filled with mineral matter? What is the origin of the dykes of modern volcanic districts?

83. How is metamorphism on the large scale supposed to have been induced? How may granite be at one and the same time a metamorphic and igneous rock?

84. Mention some of the views held with regard to the origin of mineral veins.

85. What is denudation? How do inclined strata prove that the strata have been denuded? How do faults afford proof of denudation? What have been the general effects produced by denudation on the face of the land?

86. What part have the subterranean forces acted in the formation of mountains? To what geological action is the present aspect of these mountains due? What has determined the direction of river valleys? How have the valleys, dells, &c. been formed? What effect have faults had in determining the direction of river valleys? What is supposed to be the origin of the deep rock-basins occupied by many fresh-water lakes? How is the waste of land by denudation compensated?

87. What are fossils? What is meant by petrifaction? In what kind of rocks do fossils occur most abundantly, and in the best state of preservation? and what reason can be given for this?

88. How do fossils afford proof of varied physical conditions? Give a reason for some rocks being more barren of fossils than others.

89. State some of the characters which distinguish broadly the older fossiliferous strata from those similar accumulations which are being formed in our own day.

90. How may we identify formations in separate districts? How is the interrupted and partial distribution of strata to be accounted for?