the Cheshire Rock- Salt District. 349 



To explain the appearance of the strata of indurated clay, 

 intermediate between the beds of salt, we must suppose that 

 the obstruction still continued, when the deposition of salt 

 from the waters first confined 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, pro- 

 ceeded in a great nieas-ire alone ; the salt which ren)ained 

 in the water being merely snlBcient to form small veins in 

 its substance. 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 entrance of a fresh 

 body of sea water; from the gradual evaporation of which, 

 the formation of the upper bed of rock-salt took place ; 

 and there being then no further admission of sea water to 

 the plain, the superincumbent strata of clay and marl were 

 successiv^'ly deposited in the order in which they at present 

 appear. 



This is a general sketch of the probable mode of forma- 

 tion of the Cheshire rock-salt; but as it would seem very 

 doubtful whether any single accumulation of sea water 

 could contain the materials of depositions possessing so 

 great a thickness, the theory might perhaps be successfully 

 modified, by supposing the barrier before noticed to have 

 had such an elevation in ihe progressive stages of the de- 

 position of the salt, as to allow the very frequent ingress 

 of sea water into the basin. Admitting this idea, we must 

 suppose that the formation of the strata of indurated clay 

 between the beds of rock-salt took place, either during some 

 intermission of these overflowings, or when there was a 

 great predominance of this earth in the water from which 

 the depositions were made. It seems probable too that the 

 veins of salt intersectintr iliese strata were formed rather by 

 the penetration of water holding salt in solution, from the 

 upper bed of rock-salt, than by a du'ect deposition from 

 the waters of the sea. With respect to the sources of the 

 clay, combined with the substance of the rock-salt, or 

 found in inlcrinediate and superincumbent beds, little doubt 

 can exist that it has been derived from the decomposition 

 of more ancient rocks, of the situation and precise charac- 

 ters of whicli no vestiges now remain. 



This general idea ot the formation of the Cheshire rock- 

 salt derives confirmation from the fact that, with the ex- 

 ception of the sulphate of magnesia, the same carihy salts 

 occur together with the muriate of soda in these strata, as 

 are met with in the waters of the sea. The circumstance 

 of the beds decreasing in thickness as they recede tronj the 

 Z 3 sea, 



