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



plains which are so surrounded by hills of secondary formation, as 

 to leave only a narrow egress for the waters collected on their sur- 

 face. This structure of the plain constituting the salt district of 

 Cheshire, I have particularly described ; and, regarded in its general 

 character, it leads strongly to the conclusion that the waters of the 

 sea must, at some former period, have occupied the lower parts at 

 least of the basin thus formed, which at that time had a level eighty 

 or one hundred yards lower than the one now appearing.* To 

 account for the great depositions of salt in the lower parts of this 

 basin, it is necessary to suppose that some barrier must have been 

 afterwards interposed to prevent the free communication of the 

 waters of the sea with those thus collected, and the general course of 

 the streams, the position of the beds of rock-salt, and the contractions 

 in the valley of the Weaver, which appear below Northwich at 

 Anderton and Frodsham, point out with some distinctness the place 

 where these obstructions may probably have occurred. 



To explain the appearance of the strata of indurated clay, interme- 

 diate between the beds of salt, we must suppose that the obstruction 

 still continued, when the deposition of salt from the waters first con- 

 fined, had nearly ceased ; and that at this period, the deposition of 

 clay, which had hitherto been going on in conjunction with that of 

 the salt, proceeded in a great measure alone ; the salt which remained 

 in the water being merely sufficient to form small veins in its sub- 

 stance. When these strata had been deposited to a thickness of ten or 

 eleven yards, it would appear that the barrier preventing the access of 

 the sea to the basin or plain, was again so far removed as to allow the 



* This general character of the Cheshire salt district was remarked to me by my friend 

 Sir John Stanley, in reference to the formation of the rock-salt; on which subject he 

 obliged me by some very interesting observations, which are inserted in the Cheshire 

 Report. 



