12 



been eaten away around the shaft and huge cavities formed. 

 Two instances of collapse from this cause in the immediate 

 neighbourhood of Piatt's Hill mine have occurred within 

 the last 14 years. The last one, about 5 years since, is the 

 most extensive subsidence of its kind known near North wich. 

 The existence of an old mine on the spot had been quite 

 forgotten. The greatest enemy the miner of rock salt has 

 to contend with is the fresh water. It is dangerous whether 

 in small or large quantities. At times it has burst in in 

 large quantities and drowned out the miners, destroying the 

 mine. This was frequently the case in the early days of 

 salt mining, but has not been common of late. As, however, 

 it does not spring from the solution of the salt, there is no 

 need to refer further to it. 



III. — Water descending hy gravitation to beds of salt helovj 

 the surface of the earth and reapi:)earing as brine 

 springs at the surface, but at cc higher level than 

 the salt beds. 



This is by far the most common form of water acting 

 upon beds of salt, inasmuch as the greater number of salt 

 deposits lie at considerable depths below the surface of the 

 ground. It is not however every bed of salt that is acted 

 upon by water, nor does the water act upon every portion 

 of a salt bed. The marls which invariably accompany rock 

 salt are very frequently water-tight, and then we have what 

 the Cheshire miners call a " dry rock head." In Cheshire 

 the first bed of rock salt is almost always reached by the 

 water, whilst the second bed, separated by about 80 feet of 

 very hard marl (commonly called "stone") from the first 

 bed, the water never reaches. 



Brine springs, or saline springs, are common in most parts 

 of the world, and almost invariably indicate the presence of 

 beds of salt not far off. There are however in Germany and 

 in India very weak brine springs which most probably de- 



