DRAINAGE OP IRRIGATED SHALE LAND. 



a rather broad shale ridge is shown to come in from the northwest 

 corner, becoming more sharply defined toward the south. In the 

 southwest quarter is a portion of a draw or embayment in the shale 

 formation, the slope of which is quite steep. Here the surface of the 

 water follows very closely that of the shale. In the northwest comer 

 the water conforms in a general way with the shale surface, but this 

 is a very wet seepage area and a point where the shale discharges 

 considerable water into the soil above it. It is not to be expected that 

 at such points the shale and water contours will agree closely. Far- 

 ther down on the sharp-crested portion of the ridge there is a closer 

 resemblance. 



Profile A of figure 5 (p. 29) is taken along the shale with highest 

 grade and shows a marked agreement in slope between the water and 

 shale. Profile B of figure 5 is taken across the better defined shale 

 ridge and illustrates very clearly the conformity between the surfaces 

 of the shale and water. Figure 7 (p. 33) shows the point of a well- 

 defined shale ridge. The similarity between the shale and water con- 

 tours should be noted. Profile C of figure 8 (p. 34) , taken across this 

 well-defined shale ridge, represents very much the same condition as 

 does profile B of figure 5. Profile D of figure 8 is taken along a shale 

 ridge and its point, and shows the water closely following the ridge 

 up to the sudden dip or change in grade and then passing out into 

 the soil, causing seepage conditions. 



ALKALI. 



Aside from the problem presented in the drainage of shale lands, 

 complete reclamation for agricultural purposes is further compli- 

 cated by the fact that lands of this type are often strongly alkaline, 

 so that where they have become water-logged and have been allowed 

 to lie idle for several seasons they have developed a decided alkali 

 problem in addition to the one of drainage. 



As providing a criterion for determining the severity of the alkali 

 problem of different tracts where drainage is a factor, it is believed 

 that analyses of a limited number of samples of the soil water more 

 nearly represent average conditions and consequently are of greater 

 value than are analyses of the same number of samples of the soil. 

 This view is held because the alkali in any tract of land always is 

 more or less unequally distributed, and a wide range of results will 

 be obtained from analyses of the soil, depending not only upon just 

 what parts of the tract the samples are taken from, but also upon 

 whether they represent the surface inch or surface foot or some other 

 depth of soil. It is true, there will be also a variation in the quality 

 of the soil-water from a tract, but in general the range is not so 

 great as in the soil, and a few analyses will show whether it is high 

 or low in salt content and will indicate the kinds of salts. Under 



