72 



THE IRRIGATION AGE. 



narily about 25 feet thick. In this yellow 

 clay we frequently find sheets of sand va- 

 rying in thickness and extent. Nearly.all 

 these sand sheets or " sand pockets," as we 

 sometimes call them, are filled with water. 



Under the yellow clay and above the 

 blue clay is generally a stratum of water- 

 bearing sand. Here we get what we call 

 our shallow or surface wells. In many of 

 these wells we get quite good water, in some 

 of them the water is not fit to use. As 

 these wells are supplied by water imbibed 

 from the rainfall, many of them fail in ex- 

 treme dry seasons. Yet some do not. In 

 these wells the water seldom rises above 

 where we find it. We next come to the 

 blue clay; this is about 65 feet thick. Un- 

 der this we ordinarily find a stratum of 

 sand varying in thickness from a few in- 

 ches to 30 or 40 feet. In this sand we ex- 

 pect to find an abundance of pure and 

 good water that comes rushing up, some- 

 time flowing but at the top of the well. 

 As the elevation increases and as we ap- 

 proach the hills or coteaus on either side 

 of the Jim, the water does not come so near 

 the surface. But the water always rises 

 and is abundant. Chemical analysis has 

 failed to find a trace of animal or vegeta- 

 ble impurity in this water. In some in- 

 stances there seems to be mineral deposits 

 in the vicinity of the well which renders 

 the water unfit for use. But in most cases 

 the water is pure and wholesome. 



These wells do not fail in our dryest 

 times. This fact has led some to believe 

 that these wells were at least partly sup- 

 plied by a leakage upward from the arte- 

 sian waters beneath, and there is some 

 evidence to justify this belief. The prin- 

 cipal supply is evidently the imbibition of 

 the rainfall on the highlands of the State, 

 which finds its way down into the sandy 

 stratum that underlies the blue clay, and 

 is thus stored in this vast receptacle ready 

 for man's use. 



We now come to the shale of the creta- 

 ceous formation. This blankets this en- 

 tire catch basin, and from its impervious 

 nature holds the waters down that are in 

 it and beneath it. I will not stop to des- 

 ignate between Pierre, Benton and Niobrara 

 shale, but call it all shale. As we pass 

 down through the shale we soon begin to 

 find sandy streaks; these increase in num- 

 ber and thickness until we find what is 

 known as the Dakota sandstone, which is 

 the base of the cretaceous formation. In 



the southern part of the State we find the 

 Dakota sandstone at about 500 feet; in the 

 central part of the State at about 900 feet; 

 in the northern part of the State at about 

 1,000 feet; at Jamestown, North Dakota, 

 at about 1,500 feet; at Deloraine, Mani- 

 toba, just across the boundary, they are 

 down 1 , 800 feet, and have not found it yet. 

 On the east side of North and South Da- 

 kota it abuts against the Minnesota gran- 

 ite. At the Black Hills, and all around 

 the mountain rim, it crops out. 



This Dakota sandstone is the receptacle 

 and source of our artesian waters. It 

 varies in thickness from " a few feet to 

 nearly 200 feet. The line of demarkation 

 between the shale and sand-rock is not 

 sharply drawn, the upper part being 

 nearly all shale and the lower portion be- 

 ing nearly all sandstone. We must con- 

 sider the aggregate thickness of the vari- 

 ous sandstone strata to understand its 

 storage capacity. The broken condition 

 of western South Dakota and all of Wy- 

 oming and Montana drained by the Mis- 

 souri river affords abundant opportunity 

 for the imbibition of the storm waters. 



According to the weather bureau, the 

 average annual rainfall of South Dakota, 

 taking the entire State, is about twenty 

 inches. It ranges from about fifteen inches 

 in the dryest to about twenty- six inches in 

 the wettest portions. Wyoming and Mon- 

 tana are about fifteen inches; North Da- 

 kota about eighteen inches.. In the broken 

 and rugged part of this vast catch basin a 

 large portion of this rainfall (and this in- 

 cludes snow) finds its way down through 

 the broken rocks and sandy streaks and is 

 silently stored away in the, sandstone for 

 man's use. Just how much of this water 

 is thus impounded we cannot at present 

 tell, and conjectures are idle. We do 

 know this, that the capacity of this vast 

 storage basin is beyond computation. We 

 do know that it is full to bursting, not- 

 withstanding there are vast leakages on 

 the southern border. We do know that 

 its upturned mountain rim, with its shale- 

 blanketed surface, affords the means of 

 both hydraulic and hydrostatic pressure, 

 as is evidenced every time a hole is made 

 to give it vent. 



There seems to be an arm or tongue of 

 the quartzite reaching out westward from 

 Sioux Falls by Mitchell toward Chamber- 

 lain. South of this line the pressure is 

 about fifty pounds to the square inch; 



