Tl 



each other, that locne care is required to trace the 

 demarcation between them. 



Let us consider the nature of the evidence from which 

 the existence and petition of a fault are inferred, though 

 the actual dislocai if does not appear in any 



exposure of rock. The upper part of the earth's crust 

 for a variable depth is traversed by a circulation of water 

 which, descending from the surface and performing a 



Fie. J7. - Fault (/) marked by the riw of priac* (O M U Mrfcn. 



tous underground journey, comes out again in 

 springs (;, /, s\ Fig. 37. See also p. 97). The divisional 

 planes whereby all rocks are marked serve as channels 

 along which the water oozes or flows. Of these planes 

 none offer such ready and abundant means of escape to 

 the water as lines of fault (/, Fig. 37). Hence in some 



ts the faults are traceable at the surface by lines of 

 springs. Without some knowledge of the country, we 

 should not indeed be justified in inferring the existence 

 of a fault merely from finding a linear series of springs. 

 These might arise along the boundary between two 

 different beds or sets of beds (see Fig. 23). The 

 springs which issue at the base of the English Chalk 

 are an illustration. But if, having ascertained that there 

 is no such water-bearing boundary-line in the district, 

 we come upon a marked line of springs, we may surmise 



