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that water acting as we have seen it does must inevitably 

 eat away or dissolve the rock salt in the immediate vicinity 

 of the pipe first, and as the pumping goes on and the salt 

 is abstracted, either the water will eat away the surface of 

 the salt on the line of junction between the salt and the 

 overlying marls, and thus lower slowly but surely an 

 extensive surface of salt, or it will form round the pipe 

 itself a large and deep cavity, which will enlarge itself con- 

 tinuously * I am inclined to think that both results will 

 occur, for the pressure of a column of 1,200 feet of water 

 will force the water into every cranny and crevice amongst 

 the marls, and, as in Cheshire, the surface of the salt is sure 

 to be dissolved. Again, as the fresh water will issue from 

 the boreholes, the salt in the immediate neighbourhood is 

 sure to be dissolved, as the suction up the inner pipe will 

 cause a strong current downwards and bring the water into 

 contact with the surroundino- salt. No more danojerous 

 method of mining salt can be resorted to, for the cavity 

 thus made will be in time more extensive and deep than 

 any ordinary mine, and the overlying earths will be desti- 

 tute of all support, such as pillars give to mines. As this 

 system has hitherto been only used where small quantities of 

 salt are made, and but for a limited period of time, it is not 

 safe to argue that as but little subsidence has yet occurred 

 little will occur in the future. In Germany, Quenstedt, 

 after speaking of the danger, consoled himself by saying, 

 "In Wurtemburg, owing to the thickness of the overlying 

 Muschelkalk, the danger is very small." In Middlesborough 

 they say — "Owing to the thickness of the overlying sand- 

 stone the danger is but small." It is to be hoped if the 



* Where there is much marl in the rock salt it will fall to the bottom 

 of tha cavity formed by the water and choke the blast-holes in the 

 pipes, as it did in Marshall's brine shaft in Dunkirk. This is a con- 

 tingency Middlesboro' may expect, as there is much marl in the salt. 



