14 BULLETIN 502, U. S. DEPARTMENT OF AGRICULTURE. 
the amount of water found, and whether or not pressure conditions 
exist. It is very important that none of these shale points that con- 
tribute water be missed, for, although the system may develop a con- 
siderable quantity of water from the points tapped, any remaining 
one will furnish enough water to these retentive adobe soils to prevent 
complete reclamation. 
In the drainage of those lands underlain by shale that has no dis- 
tinctive topographic features, but which is smooth and at a fairly uni- 
form depth below the surface of the soil, a system should be employed 
which has branches spaced at regular intervals and extending up the 
slope. However, the determination of the interval required for the 
branch lines necessitates a careful examination of the shale. Ex- 
perience in drilling often will enable one to determine whether or not 
the shale is traversed by systems of small crevices; the drill takes 
hold with more difficulty in shale that does not contain them than in 
shale that does. The nature of the borings brought out on the auger 
is indicative also of the presence or absence of such crevices. If the 
borings are fine-grained and more or less compact, few or no crevices 
are probable; but flaky,*mealy borings indicate the contrary. By 
those unfamiliar with the mode of occurrence of water in shale those 
zones containing water often will be overlooked, for the small lumps 
and layers of shale between the cracks are impervious in themselves, 
and the auger, passing through these, will bring up fragments of 
perfectly dry shale, while the free water frequently found between 
_ these dry borings will be thought to have collected there in pulling 
the auger out through the upper wet portions of soil. 
The existence of pressure often can be detected after having struck 
cracks in the shale containing water, by placing the ear near the hole; 
a hissing sound caused by the escape of the water from the small 
crevice into the larger opening is an almost certain indication of 
pressure conditions. The intensity of the pressure can be estimated 
by the rapidity and height of rise of the water in the well. Often the 
water will rise several feet within a few minutes, and again it may 
require a day or two for it to attain its maximum height. Where the 
water rises only a few inches, and that very slowly, the pressure is 
slight or negligible. High pressure is indicated by a rapid and high 
rise of the water. Of course, the height and rapidity of rise depend 
somewhat on the season, there being generally a seasonal fluctuation 
of the water table. In seasons of high water table, pressure strong 
enough to cause these wells to flow on the surface is encountered fre- 
quently. 
~ The borings will indicate certain spots and streaks where the pres- 
sure seems high and the water free; drainage lines should be located 
to tap these areas. Figure 1 is an example of the application of the 
information obtained from the borings. It becomes apparent at once 
