
ECONOMIC ASPECTS OF GEOLOGICAL STRUCTURE 357 
water-level in the porous beds reaches the point where the fault 
touches the surface (Fig. 135)—the conditions being somewhat 
comparable to those represented in Fig. 131. Considerable 
dislocations, indeed, will usually carry water, even although 
the structure of the rocks they traverse may not seem very 
promising. For it will rarely happen that a normal fault, 
cutting across a great thickness of rock, will not, in some 
parts of its course, truncate water-bearing beds, the fluid 
contents of which are under sufficient hydrostatic pressure to 
rise to the surface. -The faults themselves are often to some 
extent open fissures or filled with rock-rubbish which is 
easily penetrated ; while the contiguous rocks on one or both 
sides are usually more or less fractured and jumbled: it is 
not surprising, therefore, that springs should occur along lines 












FIG. 135.—HEAPING-UP OF WATER IN HORIZONTAL STRATA. 
of dislocation, under the most diverse conditions. It will 
thus be seen that a knowledge of the faults of a district is 
highly desirable, if we would understand its subterranean 
hydrography. 
Springs are usually classified as shallow or surface and 
deep-seated. A spring which fluctuates with the seasons—tepid 
in summer and cold in winter, and running full or drying up 
according as the rainfall is excessive or scanty—is obviously 
quite superficial, the water having come no great distance. 
Between temporary springs of this type and perennial springs 
whose volume remains practically constant, and whose tem- 
perature does not vary with the seasons, there are all 
gradations. Obviously, the most persistent springs derive 
their supplies from wide gathering grounds, those whose 
surface never rises nor falls probably coming from the greater 
depths, 
