146 ELEMENTARY GEOLOGY 
warm water may escape, causing a hot spring. These 
warm springs may have substances in solution which 
give them medicinal properties. Such mineral waters 
are not only drunk at the spot, but often bottled 
and widely sold. 
In its underground journey, water may pass along 
the minor cracks near the surface, until an outlet to the 
air is found. Then a:spring is produced. Quarrymen 
often encounter such springs as they quarry a rock 
from its bed; and at 
the base of cliffs they 
Brees: <=] are also common. 
SPRING 
im 
Many of the springs 
that abound in the 
hilly parts of New 
Fig. 72. England are of this 
Diagram to show conditions existing where a character. 
spring ascends through a fault plane. Perhaps the: “row 
common kind of spring in the northern United States, 
is that which depends upon differences of rock text- 
ure. for instance, if a layer of sand rests on clay, 
the less dense sandy rock allows the water to pass 
freely through it; but when the clay is reached, further 
progress is partly checked. If the clay layer is inclined, 
the water runs along the surface, perhaps coming out 
to the air on a hillside (Fig. 73). 
Whatever the class or origin of springs, it is to be 
