136 ScientifiG Proceedings, Royal Dublin Society. 



alone, while the rock-salt is extracted to a very large extent by- 

 mining. In 1879 the quantities produced in Cheshire were as 

 follows : — 



Rock-salt, .... 88,853 tons of 26 cwt. 



White salt, .... 1,087,214 „ „ 



1,177,057 



Of this 1,045,897 tons was sent down the River Weaver from 

 the North wich district, so that the j^rocess of solution and ex- 

 cavation is rapidly going on."^' 



The process may be briefly described as follows: — 



Water from the surface — consisting of a portion of the rainfall 

 and leakage from the River Weaver and other streams — finds its 

 way downwards through the strata of shale, marl, and bands of 

 stone overlying the rock-salt bed, and lodges on the surface, 

 fillina: old hollows and excavations, and dissolving the solid salt- 

 rock till impregnated to an extent varying from 21 to 25'5 

 per cent.t There are also salts, and carbonates, varying from 0"6 

 to 2*5 per cent., and the general analysis shows that the compo- 

 nents resemble those contained in sea water. The brine is being 

 pumped as fast as formed ; and as the upper surface of the bed of 

 salt is lowered, the ground above necessarily falls with it. In this 

 way the land about Northwich has subsided to the extent of no 

 less than seventy feet within the memory of man ; and it is sup- 

 posed that the top bed of salt is in some places almost entirely 

 dissolved away. The consequence is that roads, canals, railways, 

 and culverts have constancy to be banked up, and are rising 

 higher and higher relatively to houses and other buildings, which 

 subside with the surface, and are often considerably out of the 

 vertical position. Should the process above described proceed 

 till both the beds of rock-salt are consumed, a large tract of 

 country, including the valley of the Weaver, will be submerged 

 beneath the sea. 



This brings me briefly to refer to the "meres" or little lakes, 

 which form so peculiar a feature in the landscape of Cheshire. 

 These are distributed over the central plain, and are of various 



* Hunt's " Mineral Statistics " for 1879. The total produce of the United Kingdom for 

 the same year was 2,558,368 tons, of which Ireland produced 30,234 tons, 

 f According (o analyses made by Dr. Holland in 1808. 



