54 Mr. H. Holland on the Cheshire Rock-salt District. 



raised, on an annual average, fifty or sixty thousand tons of rock-salt. 

 The greater part of this quantity is exported to Ireland and the 

 Baltic: the remainder is employed in the Cheshire district in the 

 manufacture of white salt by solution and subsequent evaporation. 



It is very doubtful w^hether in any instance the body of rock-salt 

 can be considered as stratified, or disposed in distinct layers. A per- 

 pendicular section does sometimes indeed present irregular appear- 

 ances of this kind, and more especially in the purer part of the lower 

 bed, but the great body of the rock offers to the eye merely a con- 

 fused red mass, varied here and there by the occurrence of the crys- 

 talline portions of salt. 



One of the most striking facts connected with the internal struc- 

 ture of the Northwich rock-salt, is the appearance observable on the 

 surface of an horizontal section of the rock, as viewed in any of the 

 mines. On this surface may be traced various figures, more or less 

 distinctly marked, and differing considerably in the forms which 

 they assume ; some appearing nearly circular, others perfectly pen- 

 tagonal, and others again having an irregular polyhedral form. The 

 lines which form the boundary of these figures are composed of 

 extremely pure white salt, forming a division between the coarse red 

 rock exterior to the figure, and the equally coarse rock included 

 within its area. These bordering lines or rims vary from two to six 

 inches in width. The figures themselves differ greatly in size ; 

 some of them being less than a yard in diameter, others as much 

 as three or four yards ; and they very frequently are observed, one 

 within another, gradually diminishing in size to a centre. Pro- 

 fessor Playfair, in his Illustrations of the Huttonian Theory, has 

 stated, that the compression of these figures is always mutual ; the 

 flat side of one being turned to the flat side of another, and never 

 an angle to an angle, nor an angle to a side. This remark, as far 



