84 BULLETIN 502, U. S. DEPARTMENT OF AGRICULTURE. 
of both the relief and the intercepting principles of drainage as ordi- 
narily understood when applied to shale lands—this notwithstanding 
the fact that both of the tile lines were 6 feet deep and that a com- 
plete system of relief wells was installed in conjunction with lateral 
A. Particular attention is called to the:system of drainage as it 
was worked out later. This embraces branch A-1 and laterals B 
and C with their branches. Branch A-1 follows closely the lower 
margins of a broad shale point, only one edge of which is shown on 
the map. Branches B-1, B-2, and B-3 are located up the back- 
100 200 300° 400° 
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bones of three very narrow points. Branches C-1 and C-2 are located 
up the two sides of a broad shale point. Relief wells were installed 
every 15 to 20 feet along the tile lines in the shale points. This 
method of intercepting the seepage from the shale has been entirely 
satisfactory and has afforded all the relief expected. The quality of 
water developed by this drainage system has been above the average 
in salt content and is represented by sample C in Table I. 
EXAMPLE VII. 
The project shown in figure 10 is of peculiar interest in that the 
existence of the wet spot almost on the bank of the wash, 12 feet 
