268 On the Effect of Surface Tension on Chemical Action. [June 4. 
cases, greater than that of pure water, consequently the removal 
of the salts will decrease the tension. 
The rain falls upon the surface of the earth, part of it flows 
into the rivers, but another portion sinks into the ground and 
passing through the soil sinks into any porous beds that may 
lie underneath. In some formations sandstones play an important 
part, not only in constituting a considerable portion of the thick- 
ness, but also in giving character to the hills and valleys in which 
they occur; their presence can often be traced for miles where 
no single exposure of rétk occurs in the land by signs known to 
all experienced geologists; among others by the occurrence of 
springs at the foot of an escarpment. These are produced by 
the rain-water which has entered them probably at a considerable 
distance and slowly forced its way through the rock or through 
cracks until it reaches the spring. 
The action of these rocks as capillary tubes removing the 
saline matter in solution is one cause of the excellence of the 
water supply in districts where sandstones prevail. 
