Geology Part 6

29. What is the mineralogical composition of _syenite_ and _diorite_?

30. How do we distinguish the two groups into which igneous rocks are subdivided? What is meant by the terms _amygdaloidal_ and _porphyritic_?

31. Name some rocks that belong to the acidic group. What is _quartz-porphyry_?

32. Give examples of augitic igneous rocks. Name a hornblendic igneous rock.

33. What are fragmental igneous rocks? What is the difference between _trappean breccia_ and _trappean conglomerate_?

34. What is meant by the terms _stratum_, _strata_, and _stratified_?

What is the difference between _lamination_ and _bedding_? What is a section?

35. What is _false bedding_?

36. Briefly describe the general appearance of _mud-cracks_ and _rain-prints_, and say how these have been formed.

37. What is meant by a _succession of strata_?

38. Which kinds of stratified rocks generally have the greatest extension?

39. How do beds terminate?

40. How may planes of bedding sometimes indicate a break in the succession of strata?

41. What is the nature of _joints_? What are _master-joints_, and what is their probable cause?

42. What is _cleavage_, and what is its effect upon the bedding of rocks?

43. What is _foliation_?

44. Give examples of concretionary rocks. What is the nature of chert and flint nodules?

45. Define the terms _dip_ and _strike_. What is the _crop_ of a bed?

What are _anticlines_ and _synclines_?

46. What is meant by an _inversion of strata_?

47. How does contemporaneous erosion indicate a pause in the deposition of a series of strata?

48. What is meant by _unconformability_? How does unconformability prove a lapse of time between the acc.u.mulation of the underlying and overlying strata?

49. What is _overlap_?

50. What is a _fault_? What is _hade_? How are the strata affected on either side of a fault? What is the appearance called _slickensides_?

Under what circ.u.mstances should we term a fault a _downthrow_? and when should we term it an _upcast_? How is the approximate age of a fault sometimes shewn?

51. What are metamorphic rocks, and what is their general appearance?

In what districts of the British Islands are they most abundantly developed? What are some of the appearances relied upon for distinguis.h.i.+ng metamorphic from igneous granite?

52. How do igneous rocks occur? Define what is meant by _contemporaneous_ and _subsequent_ or _intrusive_ igneous rocks. How does a contemporaneous igneous rock affect the beds upon which it rests? What is the character of the bed overlying a contemporaneous rock? What is the general structure of a contemporaneous igneous rock?

What is meant by _vesicular structure_? What is the general texture of a contemporaneous igneous rock? What is the nature of the jointing in igneous rocks? What is _wacke_?

53. What is the nature of the beds of _breccia_, _conglomerate_, _ash_, and _tuff_, with which contemporaneous igneous rocks are often a.s.sociated? What is a _neck_ of _volcanic agglomerate_? How are the strata affected at their junction with a 'neck'?

54. How do intrusive igneous rocks occur? How do intrusive _sheets_ occur? What effect have they produced upon the strata above and below them? What is a _d.y.k.e_? What relation do they occasionally bear to _sheets_ of igneous rock? What is a _neck_ of intrusive igneous rock, and how have the strata surrounding it been affected?

55. Mention some of the contrasts between _intrusive_ and contemporaneous igneous rocks. What alteration is produced upon coal with which an intrusive sheet has come in contact?

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 interst.i.tial water. What is the origin of _travertine_ or _calcareous tufa_?

60. How have _stalact.i.tes_ 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 a.n.a.lyses 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 _creva.s.ses_, 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 sh.e.l.ls 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 acc.u.mulate? What effect have the tides and ocean currents in the distribution of sediment?

71. What is the general rule as regards fine-grained and coa.r.s.e-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 sh.e.l.l-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?