are produced by little streams issuing from cracks in a rock, through 

 which the water has sunk. 



In the preceding we have supposed that clay or an impermeable 

 material through which the water will not pass comes out to the sur- 

 face on a side hill near the bottom of a valley. But this may not be 

 the case. The valley may not go deep enough to reach that layer. 

 How, then, shall we get at the water? Evidently we must make an 

 opening down to it. Such an opening is a well. In an ordinary well 

 we know that the water has to be raised by a pump or bucket, but 

 there are others called artesian wells, which require no bucket or 

 pump, for the water, when we once reach it, rushes up to the surface. 

 What is it that produces some kind of pressure below and forces the 

 water up? If we covli see down an artesian well we would find that 

 at its bottom there is water confined in a permeable substance like 

 sand by one layer of an impermeable substance like clay above and 

 another impermeable layer below. Now, let us in imagination start 

 from the bottom of the well and follow this sand layer. We will find 

 that it slopes upward, and at a great distance comes out on a hillside, 

 where it catches water when it rains. This water runs down through 

 the sand, being prevented from escape by the two impermeable layers, 

 and accumulates in the sandy layer so as to produce great pressure. 

 When this reservoir of water is tapped by the hole bored down, the 

 water rushes up with great force. If you wish to see how such action 

 takes place punch a small hole in the bottom of a tin can (say a two- 

 pound coffee can) and after half filUng a bucket with water, push the 

 can down into the water and notice how the water spurts in through 

 the hole, rising nearly to a height of the water in the pail. 



There are many other interesting kinds of springs, such as hot 

 springs and springs that sometimes stop and then start again every 

 few hours, but as you may not hear of any in your neighborhood, we 

 shall only say a few words about them. The water that comes from a 

 hot spring is often very warm. It has in fact been heated by the 

 great heat" there is deep in the earth. A miner will tell you that the 

 earth grows about one degree hotter for every sixty feet he descends. 

 Now, some water that falls on the surface of the earth finds cracks 

 in rocks, especially Umestone, and passes down in all kinds of zigzag 

 directions until for some reason it can get no further, when it turns 

 around and comes up by another series of zigzags. Having gone to 

 a great depth, it is greatly heated and when it finally reaches the sur- 

 face it is still 'very hot and gives rise to a hot spring. The other kind 

 of spring mentioned that starts and stops in a very mysterious fashion 

 is difficult to explain, so I shall not attempt to account for it here. 



