Book III. 



DRAINING BOGS. 



629 



general be accomplished by means of levelling and carefully attending to what has been 

 already observed respecting the formation of hills and elevated grounds, and by inspect- 

 ing the f)eds of rivers, the edges of banks that have been wrought through, and such pits 

 and quarries as may have been dug near to the land. Rushes, alder-bushes, and other 

 coarse aquatic plants, may also, in some instances, serve as guides in this business ; but 

 they should not be too implicitly depended on, as they may be caused by the stagnation of 

 rain-water upon the surface, without any spring being present. The line of springs 

 being ascertained, and also some knowledge of the substrata, a line of drain {Jig. 484 6, h) 

 should be marked out above or below them, according to the nature of the strata, and 

 excavated to such a depth as will intercept the water in the porous strata before it rises to 

 the surface. The effect of such drains will often be greatly heightened by boring holes 

 (c) in their bottom with the auger. Where the impervious stratum [Jig. 485 aj, that 



lies immediately beneathjhe porous {h), has a slanting direction through a hill or rising 

 bank, the surface of the low lands will, in general, be spongy, wet, and covered with 

 rushes on every side (c). In this case, which is not unfrequent, a ditch or drain (d), 

 properly cut on one side of the hill or rising ground, may remove the wetness from both. 

 But where the impervious stratum dips or declines more to one side of the hill or eleva- 

 tion than the other, the water will be directed to the more depressed side of that stratum ; 

 the effect of which will be, that one side of such rising ground will be wet and spongy, 

 while the other is quite free from wetness. 



3931. Where water issues forth on the surface at more places than one, it is necessary to 

 determine which is the real or principal spring, and that from which the other outlets are 

 fed ; as by removing the source, the others must of course be rendered dry. When on the 

 declivity or slanting surface of the elevated ground from which the springs break forth, 

 they are observed to burst out at different levels according to the difference of the wetness 

 of the season, and where those that are the lowest down continue to run, while the higher 

 ones are dry, it is, in general, a certain indication that the whole are connected, and 

 proceed from the same source ; and consequently that the line of the drain should be 

 made along the level of the lowermost one, which, if properly executed, must keep all 

 the others dry. But if the drain was made along the line of the highest of the outlets, 

 or places where the water breaks forth, without being sufficiently deep to reach the level 

 of those below, the overflowings of the spring would merely be carried away, and the 

 wetness proceeding from that cause be removed ; while the main spring, still continuing 

 to run, would render the land below the level of the bottom of the drain still preju- 

 diciously wet, from its discharging itself lower down over the surface of the ground. 

 This, Johnston states, was the custom, until Elkington showed the absurdity of the 

 practice of drainers beginning to cut their trenches wherever the highest springs showed 

 themselves between the wet and the dry ground, which not being of a depth sufficient to 

 arrest and take away the whole of the water, others of a similar kind were under the 



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