10 Tattersall & Coward, Fauna of Rostheme Mere. 



melting of the salt proceeded most rapidly, there the sub- 

 sidence would be greatest. It may thus have happened, 

 at least in some cases, that hollows in the surface of the 

 ground thus produced have given origin to the lakes of 

 Cheshire, and to this cause Mr. Ormerod appears inclined 

 to attribute Budworth Mere and Pickmere, which lie a 

 short distance to the north of Northwich, and certainly 

 within the limits of the great beds of rock salt " 



This theory, suggested by Ormerod 

 Origin of the Mere, and upheld by Hull, has been 

 generally accepted. It is largely 

 supported by the subsidence of land, noticed many 

 years ago and still going on, in those parts of the Cheshire 

 basin where brine is artificially pumped. The main subsi- 

 dences are above the actual rock salt mines, into which, 

 after much of the rock salt has been removed, water is 

 allowed to flow, dissolving the remaining beds and the 

 pillars which were left to support the roof of the levels. 

 When this is pumped out as brine there is usually a surface 

 subsidence. It is argued, reasonably, that dissolution of 

 salt has been in operation naturally for ages, for brine 

 springs were known centuries before rock salt was dis- 

 covered. Water constantly percolated through the marls 

 and reached the salt seams, slowly dissolving the salt, and 

 natural subsidence was liable to follow whenever the 

 water was not in sufficient quantity to support the upper 

 strata. No more satisfactory explanation of the formation 

 of these deep, rounded, cup-shaped Cheshire hollows has 

 been suggested. 



Reference to the map of Rostherne Mere, which we 

 have prepared, shows that its bed consists of two distinct 

 depressions, a large southerly one (the main lake basin) 

 and a small northerly one. We accept Ormerod's ex- 

 planation of subsidence, consequent upon the dissolution 



