bad the pipe could be surrounded, and covered for about four inches, 
with coarse gravel or crushed rock, and the trench filled with earth 
other than clay. It is necessary to make systematic borings with a 
6 '' augur to determine the direction of flow- in the soil. Here this 
often follows an almost vertical direction, causing the trendies to be 
very close or very deep. As a rule, however, the main tile follows the 
course of a small stream, with feeders coming in from the side seeps. 
Plere the problem is to lay a pipe, as a general rule through stiff clay, 
so that a considerable torrent can pass over it, and such that a few 
hours after it will remove every drop of water and suffer no damage 
from erosion. Such a pipe has of necessity to pass silt in quantities 
during freshets. Experience has shown that a & pipe will 
satisfactorily pass silt at a grade of one per cent, and a lo'' pipe at a 
grade of one-half per cent. These grades can be made ‘flatter if 
a head can be obtained to act on the pipe, but should be avoided if it 
is possible. Should ‘ flatter ’ grades be required, concrete ditches or 
stone ditches set in cement mortar should be used. 
In starting operations on a valley, the first thing to study is the 
best method of straightening the stream with a view to getting greater 
fall and a shorter distance. If the grade exceeds 5 cent., small 
waterfalls should be introduced to break the velocity over the surface, 
during floods. The pipes should be laid at least 2' &' below the bed 
of the stream, the trenches should be carefully graded with an 
instrument and the pipes laid evenly and true, with joints open to 
the extent of to They should be firmly imbedded in crushed 
rock on all sides, e.xtending at least 4/' above the tile. Rock, broken 
to about 4" cubes, should then be filled in, up to near the surface, and 
the last layer finished off in heavy stone if the scour is great. Some 
small stone must be placed at the top to prevent a too free entry of 
silt in the first rains. All side branches should be treated in the same 
way, and should connect to the main with Y junctions. When 
surface water has to run in volume over the pipe, the outfall should 
be carefully planned so as to pass the water away quickly, and should 
be strong enough to stand the scour that occurs at this point 
It would appear probable that after a short time the porous stone 
placed over the pipe would completely clog, but this does not 
occur. What happens is that the first heavy rains completely cover 
the stone with about 2'' of coarse granular earth. The grass quickly 
