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ley springs and tlie 8tone spring (Bloomington water-works) near Bloom- 

 ington. Ill some cases this layer might be made to serve as the substra- 

 tum of a pond. Great care would then be necessary to make the sides of 

 the pond secure, since they would be in an extremely cavernous part of 

 the formation. .Second, for ponds to be fed by springs of the type just 

 mentioned, the top of the Ocilitic limestone can be utilized for the bottom 

 of the pond, and here again the sides of the pond must be made secure. 

 The second pond of the Bloomington water-works is built on this layer, 

 and all of the leakage is through the valley sides, and not through the 

 floor of the pond. Where the valley sides are thickly covered with residual 

 clay, and this is carefully puddled, ponds at this level should be fairly 

 tight. Third, in a few cases the flow of the larger springs of the region, 

 or of several springs combined, will be sufficient for small towns, without 

 impounding. In such 'ases the flow of the springs should be veiy care- 

 fully gaged, throngh a period of years, before any money is spent on works 

 to utilize the water. 



In this connection it is proper to speak of the special characteristics 

 of the springs of the limestone region, especially since they are usually 

 very much overrated, and their nature and cause misunderstood. All of 

 the large springs of the limestone region are the outlets of subterranean 

 solution channels in the rock, and very often serve also as the mouths 

 of well-defined caves. These caves and channels are in turn, as already 

 shown, intimately connected with the sinkholes of the region. The sink- 

 holes are the main gathering grounds of the waters that emerge at the 

 springs. Or, to be more precise, they are the avenues through which the 

 v.ater is taken under ground. The sinks, like the caves themselves, are 

 largely the work of solution. (See Fig. S.) Where the sinks are open at 

 the bottom, as is usually the case, storm water passes very readily and 

 very quickly into the subterranean channels, and as quickly emerges at 

 the springs. At such times the spring water is muddy, showing that it 

 is merely surface water that has made a journey of gi'eater or less lengtii 

 through an underground conduit. It is indeed possible in some cases to 

 drop a handkerchief into a sinkhole, and to presently see it emerge at a 

 distant spring. Sometimes the journey from the sink to the spring is very 

 short, a few rods ; at other times it may be many miles. In any case the 

 storrn water conies to the sjiring unfiltered. 



