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Indiana University Studies 



precipitation of the excess mineral matter which can no longer 

 be held in solution because of the weakening of the carbonic 

 acid. 



Solubility of Limestone 



It is well established that calcium carbonate is nearly in- 

 soluble in pure water, but that it is readily attacked by car- 

 bonic acid (H0CO3) and converted into calcium bicarbonate, 

 H.,Ca (CO3) o , which is quite soluble in water. Thus, since lime- 

 stone is made up, for the most part, of calcium carbonate, it 

 may be almost entirely removed by solution, leaving a residual 



Fig. 19. — Limestone bowlder channeled by water containing 

 carbon dioxide, illustrating the occurrence of differential 

 solution similar to that required in the development of 

 stylolitic phenomena. (From Cleland's Geology.) 



clay composed of the less soluble, minor constituents of the 

 rock — principally silica, alumina, oxides of iron, with small 

 quantities of soda, potash, magnesium carbonate, and calcium 

 carbonate which have not been completely dissolved. In the 

 case of limestone, instead of there being a gradual transition 

 from fully-formed residual clay into the parent rock, the 

 passage from the clay to bed rock is sudden. The reason is 

 that the clay is left as a residue from solution, and not from 

 a gradual chemical breaking down and change of the minerals 

 of the rock, as in the case of granites, etc. Thus a small thick- 



