Mr. H. Holland on the Cheshire Rock-salt District. 57 



day a few inches In thickness. Much, however, it is evident, must 

 depend upon the number of the beds thus disposed, but this I do 

 not find any where noticed. The earthy saline contents of the 

 foreign rock-salt very exactly resemble those of the Cheshire ; the 

 gypsum existing in much larger proportion than the other earthy 

 salts, and appearing in considerable masses, both distinctly, and in 

 mixture with the beds of clay. It is an important fact, however, 

 'that sea-shells and other marine exuvise are found in these beds of 

 clay and gypsum ; a circumstance which, as I before stated, never 

 occurs in the Cheshire mines. It would seem that the portion of 

 oxide of iron combined with the clay in the substance of the 

 English rock-salt does not exist in the mineral as found abroad, 

 or at least in a proportion not so considerable. 



The comparative commercial value of the English and Polish 

 mines is best ascertained by the fact that many thousand tons of 

 rock-salt are annually sent from Cheshire to the parts of the Prussian 

 coast most nearly adjacent to the salt-mines ; independently of the 

 large supplies of the English manufactured white salt which are ex- 

 ported to the same country. 



Considerations on the Origin of the Cheshire Rock-salt. 



With respect to the theory of the formation of rock-salt, as appli- 

 cable particularly to that of Cheshire, I shall not venture to say much, 

 and that little will be of a general nature. Though it must be ac- 

 knowledged that there are some difficulties connected with the suppo- 

 tion, little doubt can exist of the general fact, that the beds of this mi- 

 neral have been formed by deposition from the waters of the sea. Such 

 an opinion acquires much probability from the situation in which 

 these beds usually occur j occupying the vallies and lower parts of 



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