VIIT. INFLUENCE OF FAULTS. 93 



land, was sudden, though there may be exceptional cases. These 

 great mechanical effects were the result of continued pressures on 

 materials always in some degree flexible, for no rocks are abso- 

 lutely incapable of yielding to force. These pressures were for 

 the most part exerted in very wide areas of work, during periods 

 of long duration. In the course of these periods, and in some 

 districts, the accumulated strain was relieved, and the flexures of 

 the strata were changed into fractures. We term these interrup- 

 tions of continuity ' faults,' and they are justly regarded as me- 

 chanical effects produced in a short time, or even suddenly, as by 

 a sharply cut fissure, on one side of which the strata were elevated, 

 on the other side depressed. 



Diagram XXIV. Deposits against a fault. 



In the above diagram the plane of a fault, by which pressure 

 was relieved, is marked by f, and displacement is conceived to 

 have occurred on the face of a sea-cliff, H being the sea-level, as 

 before. 



The deposits of pebbles, sand, and clay will in this case be 

 nearly as in the former example ; except that against a high cliff, 

 with deep water, the rocky fragments will have more of a brecciated 

 character, and be accumulated to a greater thickness. Thus may 

 be understood the thick magnesian conglomerates and breccias, 

 at the foot of the great Ingleborough fault ; and the equally thick 

 Permian accumulations of like nature and nearly equal antiquity 

 along the eastern side of the Malvern and Abberley Hills. In each 

 case the fragments are mainly, if not wholly, derived from the hills 

 on the line of the fault, though not necessarily from the imme- 

 diately opposite fronts of the hills. 



