16 



Afghanistan frontier, there are large "pot holes" of a crater 



shape in the rock salt district, and these have been 



attributed to the solution of the underground salt.* One 



great difficulty that occurs to me is that the meres in 



Cheshire and the " pot holes " in Kohat are all completed 



works. There are no meres and pot holes as far as I can 



learn now forming naturally. I say " naturally," for I shall 



soon have to speak of artificial meres and " pot holes " also, 



though not in Kohat, being formed at the present time. 



An attempt was made recently before a Committee of the 



House of Commons, and in a paper read before the British 



Association by a well-known geologist, to prove that the 



great subsidences occurring in some parts of Cheshire are 



caused by fresh water reaching the salt beds, becoming 



saturated, and escaping in springs. This was an attempt to 



demonstrate that nature is progressing by leaps and bounds 



at the present time, after having through previous historic 



ages lain practically dormant, although there can have been 



no alteration whatever in the real agent or in its action 



during the whole period. 



It is not difficult to understand why natural brine springs 

 should as a rule be weak, or if strong not copious. The 

 same rule applies to a brine spring as to any other spring. 

 The source which causes the outflow must be at a higher 

 level than the outflow itself In the case of brine the 

 source must be higher in proportion to the salt content 

 of the spring. The specific gravity of saturated brine as 

 compared with fresh water is as 12 to 10; consequently 

 it needs a column of 12 feet of water to balance a column 

 of 10 feet of brine. That is supposing, of course, that 

 we had an inverted perfect syphon, and not reckoning 

 friction. However, we never have a perfect syphon, and 



* As these " pot holes " are formed in a district where the rock salt is 

 at the surface and crops out, and where the di'ainage of the water forms 

 springs at a lower level, they properly belong to the preceding section. 



