290 • BOARD OF AGRICULTURE. [Jan., 



surface, and if wells are to be successful they must be sunk 

 deeper. The fluctuation of the water table with the supply of 

 water is well shown in irrigated regions. Here the supply is 

 artificial, in other cases it is natural, but the result is the same, 

 and wells sunk in such a region will be dry part of the year 

 unless they reach a depth below the dry water table. 



The water contained in the ground does not remain sta- 

 tionary, but wherever the land is above the level of the sea it 

 has a drift or underground flow, usually in a definite direction. 

 This motion of ground water is rarely in the shape of a definite 

 stream ; only in limestone regions where underground drainage 

 has been established do such phenomena occur. In extreme 

 cases, as in parts of Kentucky, all the water flows underground 

 and the surface channels are dry over many square miles. In 

 the case of Kentucky this absence of surface water appears to 

 be no drawback, for other beverages supply the lack, but it is 

 a decided defect in the scenery. Ground water generally forms 

 no streams, but moves gradually and finds its way between the 

 grains comprising the rock. The rate of movement is very 

 slow indeed. In fine sand with a slope of ten feet to a mile 

 ground water will move 52 feet per year. In fine gravel it 

 sometimes attains a speed of a mile a year. By suitable study 

 it is possible to determine the rate and direction of motion of 

 the ground water for any given place. The movement of 

 ground water has an important relation to health. Noxious 

 water may flow for some distance before being purified by 

 natural filtration, especially if it has occupied the same course 

 for many years, and care should be taken in the location of 

 wells. In 1872 a typhoid epidemic broke out at Lausanne, 

 Switzerland, and it was found that the polluted water had 

 traveled through a mile of sands and gravels. 



Ground water is returned to the surface naturally by 

 springs, or artificially by wells of various sorts. Springs are 

 usually due to one of three causes : they may be outlets for 

 subterranean streams, like Silver Spring, Florida, or Cascade 

 Spring, South Dakota ; they may be located along some crack 

 in the earth's crust and thus be outlets for very deep water 

 supply, like the mineral springs of Virginia, and many Con- 

 necticut springs ; and finally they may occur at the contact be- 

 tween strata of open texture and water-tight layers. Probably 

 90 per cent, of all springs belong to this last class. The water 



