Mr. H. Holland on the Cheshire Rock-salt District. 49 



salt is at least twelve or thirteen yards below the low-water mark of 

 the sea at Liverpool ; a fact perhaps not wholly unimportant as 

 regards our ideas of the formation of this mineral. 



The thickness of the upper bed of salt at North wich has been 

 already stated to vary from twenty to thirty yards : that of the 

 lower bed has never yet been ascertained in any one of the mines in 

 this district. The workings in this lower stratum are usually begun 

 at the depth of from twenty to twenty-five yards, and are carried 

 down for five or six yards, through what forms, as will afterwards 

 be mentioned, the purest portion of the bed. In one of the mines 

 e shaft has been sunk to a level of fourteen yards still lower, with- 

 out passing through the body of rock-salt. We have thus an ascer- 

 tained thickness of this bed, of about forty yards, and no direct evi- 

 dence that it may not extend to a considerably greater depth. 



Though only two distinct beds of the fossil salt have been met 

 with at Northwich, it has been ascertained that the same limitations 

 do not exist throughout the whole of the salt district. At Lawton, 

 near the source of the river Wheelock, three distinct beds were found, 

 separated by strata of indurated clay ; one, at the depth of forty-two 

 yards, four feet in thickness ; a second, ten yards lower, and twelve 

 feet thick ; and a third, fifteen yards still further down, which was 

 sunk into twenty-four yards, without passing through its substance. 

 Coal is found and worked within two or three miles of this place, 

 and the only limestone known in the County of Chester, is got from 

 the hills which here form the southern boundary of the plain. In 

 no other parts of the salt district, than at Northwich and Lawton, has 

 the upper bed of rock been worked through. 



The strata passed through in going down to the upper bed of 

 rock, are nearly horizontal in position, and very uniform in their 

 structure, consisting in every instance of beds of clay and marl j and 



G 



