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 accumulation 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 circumstances 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 distinguishing 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 wacké?
53. What is the nature of the beds of breccia, conglomerate, ash, and tuff, with which contemporaneous igneous rocks are often associated? 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 dyke? 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?