128 OUT! l\l SOI FIELD GBO1 < I PARTI 



of our subject will. I hope, convince liiin that the mere 

 visible section of a fault on some cliff or shore docs not 

 afford by any means such dear evidence of its nature 

 and effects as may IK- obtained from othrr parts of the 

 region where it may not show itself at tin- surfnre at all. 

 In fact, he might be deceived by a single section with a 

 fault exposed in it, and might be led to regard that fault 

 important and dominant one, while it might be 

 only a secondary dislocation in the near neighbourhood 

 of a great fracture, for which the evidence would be 

 elsewhere obtainable, but which might never be seen 

 itself. The actual position (within a t. \\ yards) of a 

 large fault, its line across the country, its effect on the 

 surface, its influence on geological structure, its amount 

 of vertical displacement at different parts of its course 

 all this information may be admirably worked out, and 

 yet the actual fracture may never be seen in any one 

 single section on the ground. A visible exposure of the 

 fracture would be interesting ; it would give the exact 

 position of the line at that particular place ; but it would 

 not be necessary to prove the existence of the fault, nor 

 would it perhaps furnish any additional intormation of 

 importance. 



The geologist, therefore, constantly finds evidence of 

 far more dislocations than he can actually see. Those 

 which appear, sometimes commonly enough, on lines of 

 cliff or coast-section, are apt to be but small and trifling. 

 The larger faults those which powerfully influence the 

 geological structure of a country are seldom to be 

 caught in any such visible form. Now why is this? 

 tl reasons may be assigned, each of weight 



