136 TILE DRAINAGE 



known. The desert soils where irrigation is practiced, are 

 so loose and porous that the ground is really underdrained by 

 nature. In fact, in many places they have great trouble in 

 conveying the water in irrigating- ditches, the soil being so 

 porous that the greater part of the water is lost before it goes 

 to where it is wanted. In fact, at Riverside they are ce- 

 menting the bottom and sides of the irrigating-canals, and 

 this is being done very largely. Now, in such soils, and 

 especially where there has never been a surplus of rains, 

 except for a brief period in the winter time, underdraining 

 would seldom pay expenses. And this leads us to a method 

 of getting an outlet for underdrains that has already been 

 touched upon. In the vicinity of Mammoth Cave, water 

 never stands in hollows or depressions. In fact, in passing 

 along on the railroad we see hollows between the hills, with- 

 out number, and no visible outlet anywhere. After very 

 heavy showers the water will sometimes stand in these 

 basins for a few hours ; but it usually goes down through the 

 porous soil and through the porous rock almost as rapidly 

 as it collects in the basin between the hills. In some 

 cases I saw considerable streams go down into such a hollow 

 in the hills, and disappear in a sink-hole that resembled a 

 well without any bottom to it. The water had probably 

 found a passageway into some of the caverns that underlie 

 that large tract of that Mammoth Cave country. Now, in 

 localities where there are no caves, there are frequently por- 

 ous strata of gravel that act in much the same way ; and in 

 such places an outlet for underdrains may be found by simply 

 digging a well down into this gravel. Even here in our hard 

 clay subsoil, with soapstone underlying, we drilled a well 

 that we found, by actual test, would take quite a stream of 

 water, when it was once turned into it, immediately out of 

 sight. A good many times it may be worth while to experi- 

 ment in this way, where it is desirable to get an outlet for 

 surplus water. On page 104 we are told how friend Terry 



