PROPERTIES OF WATER AND SOURCES OF SUPPLY. 19 



a typical example of the way chalk beds are found. 

 Many towns will be found to have arisen on the 

 lower parts of the flat slope, by reason of there being 

 water readily at hand here, and primitive man, not 

 being usually a skilled engineer, founded his dwelling 

 where water existed, in opposition to present-day 

 methods of calling in the engineer to bring it from 

 a distance. It will be noted, too, in fig. 6, that no 

 water will be obtained on the escarpment side, be- 

 cause the impervious stratum of marl has a gradual 

 slope in one direction, but if it has also a slope to- 

 wards the escarpment side, which is sometimes found, 



Greenland 



FIG. 7. 



then, although the slope will be the shorter of the 

 two, a small amount of water may be had there as 

 well where the marl outcrops on the escarpment side. 

 In the same way a fault, as shown by fig. 7, will cause 

 a similar supply, but the line xy must slope in the 

 direction^ to an extent enabling hydraulic laws to 

 be fulfilled. Below xy the ground will be saturated. 

 Generally it will be found that chalk springs occur 

 in valleys much below the general level of the forma- 

 tion, and their overflow corresponding with the ex- 

 istence of some fissure above a harder and more 

 retentive bed than the mass of chalk. 



Almost as absorbent as chalk are the oolitic rocks. 



