the Cli£shire Rock- Salt District. . 339 



and forty vears ago, in searching for coal.. This bed of 

 rock was the only one worked for more than a century, 

 when, in the same neighbourhood, a second and inferior 

 stratum was met with, separated by a bed of indurated clay 

 from the one previously known. This lower stratum was 

 ascertained to possess at a certain depth, a great degree of 

 purity and freedom from earthy admixture; on which ac- 

 count, and from the local advantages of Northwich for ex- 

 portation, the fossil salt is now worked only in the vicinity 

 of this place. 



This local limitation of the mines precludes the possibi- 

 lity of many comparative remarks which might be interest- 

 ing to the geologist; and in giving a particular description 

 of the rock-salt formation, I must confine myself in great 

 measure to the facts which present thernselves in the neigh- 

 bourhood of Northwich, explaining first the circumstances 

 of general position, &:c. and then entering into the more 

 minute particulars of the mines which have been sunk into 

 these important strata. 



The rock-salt of Northwich occurs, as I have just men- 

 tioned, in tw o great strata or beds, lying nearly horizontally, 

 but on different levels, and separated, the superincmnbent 

 from the subjacent stratum, by several layers of indurated 

 clay or argillaceous stone. These intervening beds possess 

 in conjunction, a very uniform thickness of ten or eleven 

 yards, and are irregularly penetrated by veins of the fossil 

 salt. Though the evidence on the subject is not entirely 

 of a positive nature, there seem strong grounds for believing 

 that the beds of rock-salt at Northwich are perfectly distinct 

 from any others in the salt district , forming what the Ger- 

 mans would call Uegende stbcke, lying bodies or masses of 

 the mineral. It will readily be conceived that there is 

 much difficulty in acquiring precise inforrnation with re- 

 spect to the extent and limitation of these great masses, 

 and that there are many sources of error to which such an 

 inquiry is liable. There are, however, a few leading facts 

 upon which dependence may be placed, and which will be 

 admitted to furnish fair grounds for deduction. 



It w^ould appear that the great beds of rock*-salt at North- 

 wich assume a general longitudinal direction from north- 

 east to south-west, the line which has been traced upon 

 them in this direction being a mile and a half in length, 

 and no direct evidence existing that they may not extend 

 further in these points; wiiile their transverse extent, as 

 measured by a line at right angles to the ionner, is much 

 more limited, probably r\ot exceeding in atiy place one thou- 

 sand 



