68 TILE DKAINAGE. 



soak into it equally well from both sides, as in Fig. 18, of 

 course soaking forward down the slope (underground) 

 slightly, rather than at an exact right angle from where 

 it soaks into the surface. 



It might be supposed that the water from twice as much 

 space would soak down hill into the tiles (as in Fig. 18), as 

 on level ground ; but, practically, no more will do so. The 

 u suction range " of a tile drain depend more upon the po- 

 rosity of the soil than upon the degree of the slope. Not 

 only is this true theoretically, but I find it practically true, 

 as already stated in connection with Figs. 9 and 10, where 

 we saw that a drain up hill from a row of apple-trees helped 

 the trees very little. 



One point more. The plowing of a thoroughly tiled field 

 should leave no dead furrows tor surface-water to follow. The 

 entire surface should be as level and free from depressions 

 as possible ; then the rains and melted snows will soak 

 straight down into the soil, and reach the drains largely by 

 pressing up from the lower level. If you dig a ditch in a 

 wet time you will see the water ooze slowly up from the 

 bottom of your ditch as you dig it or soon after it is dug 

 in clear ^rnall streams. This shows exactly how and where 

 the water should enter the drains; viz., from below, under 

 the force of hydrostatic pressure. Let me speak still more 

 fully of the porosity of the soil and subsoil as affected by 

 their stratification. Most of our subsoils, and especially the 

 alluvial and drift subsoils, as before remarked, lie in layers 

 or strata, nearly or quite horizontal. Examine fresh railway 

 cuts for a few miles through such soils, or dig tile drains for 

 a few weeks in bowlder clay, and you will see. That is, 

 these soils are more porous horizontally than perpendicularly. 

 Especially in bowlder clay I have often noticed "seams," 

 layers, or "pockets" of sand or gravel, from which the 

 water bubbles up or seeps in as soon as you remove the im- 

 prisoning clay that binds it. Now, although the soils that 

 need drainage are most porous side wise (or horizontally), 



