THE LINE OF DESCENT. 107 



upon this stratum, and as borne out by it to the 

 surface. 



"A drain down the slope gives to the water borne 

 up by these strata an outlet of the depth of the 

 drain. If it be four feet, it cuts the water-bearing 

 strata each at that depth, and takes off the water. 

 In these cases the different layers of clay, or other 

 impervious partings, are like the steps of a huge 

 staircase, with the soil filling them up to a regular 

 grade. The ditch cuts through these steps, letting 

 the water that rests on them fall off at the ends, 

 instead of running over the edges. 



" Now, looking at the operation of drains across 

 the slope, and supposing that each ditch is draining 

 the breadth next above it, we will suppose the drain 

 to be running full of water, what is there to prevent 

 it from passing out of that drain in its progress at 

 every joint of the tile, and so saturating the breadth 

 below it 1 Drain-pipes afford the same facility for 

 water to soak out at the lower side as to enter on 

 the upper, and there is the same law of gravitation 

 to operate in each case. 



"Mr. Denton says: 'With respect to the direction 

 of drains, I believe very little difference of opinion 

 exists. All the most successful drainers concur in 

 the line of the steepest descent as essential to effi- 

 ciency and economy.' 



" To produce perfect drainage of a portion of this 

 land, which we wdll suppose to be a gentle slope, 



