FAULTS. 39 



of slippage often exceeding in amount the throw of 

 genuine faults." 



Some slips are evidently due to a sliding along 

 an oblique master joint. Such a slide has taken 

 place on the north side of Ban try Bay, County Cork, 

 immediately west of Pulleen Harbour, a tract of 

 country a mile long, and about a furlong wide, 

 having slipped out seaward. Artificial landslips are 

 caused by coal mining and the like; large areas of 

 land subsiding into the vacancies left by the sub- 

 traction of coal, iron ores, clay and other minerals ; 

 while natural subsidences have taken place during 

 earthquakes, such as that which took place at 

 Lisbon. 



Landslips teach us how faults on a small scale can 

 be formed at the surface of the earth, and from them 

 we can reason on the formation of most of the deep- 

 seated faults ; all being due to movements along lines 

 of least resistance, which must be master or other 

 joint-lines. 



