SUBTERRANEAN CHANNELS. 43 



will either stand in ruts and puddles until sucked up 

 by the air, or run away to feed the nearest ditch, or sink 

 through some bed of sand at a distance. But though clay 

 usually lets but little water pass through, yet it parts with 

 so much of its own moisture in hot dry seasons that it 

 gapes in all directions, and when the rain comes much 

 of it escapes through these cracks. 



In one way or other, then, a great deal of rain sinks into 

 the ground, and when its downward progress is arrested by 

 some impenetrable bed, it soaks through the soil sideways, 

 and sometimes travels many miles before it finds an outlet, 

 while, by dint of often using the same road, it frequently 

 wears for itself an open channel, along which it flows as 

 rapidly as the rivers above ground do in theirs. That 

 this must be the case is evident from the fact that a large 

 increase of water is observed in certain wells and fountains 

 (as, for instance, at Nismes), so soon after rain has fallen 

 some miles off that it is impossible it should have passed 

 through soil, however porous. Moreover, in some places 

 the water from time to time throws up seeds, vegetables, 

 fresh-water shells, and even fishes, which have evidently 

 travelled a long way underground, as much sometimes as 

 one hundred and fifty miles, and this, of course, can only be 

 by open channels. 



Where such channels do not exist the water spreads 

 about in all directions in search of an outlet, which it finds, 

 perhaps, in the face of a cliff, the side of a hill, or at 

 the bottom of a slope so' trifling as not to deserve the 

 name of hill. Where, however, the whole face of the 

 country is as flat as a table, there, of course, no springs 



