^40 A Sketch of the Natural History of 



sand three hundred or one thousand four hundred yards. 

 Several circumstances concur in uiving probabiHty to this 

 siatemcnt. Let iwo parallel lines, drav. n tronn NE to SW, 

 with an iniervenuia; distance eqi;a! to about half their 

 lenath, be enipinyed to designate the supposed extent of 

 the subjacent rock-salt. In a mine which approaches very 

 nearly to the eastern limit of the area thus formed, the 

 upper bed of rock-salt was actually worked through in an 

 honzonial direction on this side, and discovered to be going 

 off vMth a very rap^d declivity. A similar fact has been 

 Stated with respect to another pit further to the south on 

 the same line ot boundary ; but as the mme was destroyed 

 manv vears aj:o by the ingress of fresh water, ihis statement 

 is considerably iTK.re doubtful than the former. It may be 

 remarked too, that in sii^king for brine a little beyond, or 

 out ot the area, on this side, the brine met with is of a very 

 weak and inferior kind, and at a short distance altogether 

 disappears. Appearances leading to the same conclusion 

 of the sudden terniiiiaiion of the body of rock salt occur 

 on the opposite side of the area marking its extent. In a 

 mine at the northern extremity of the western line of 

 boundary, a sha!t situated nearer to this line is fifteen yards 

 deeper than another shaft immediately contiguous, ap- 

 parently in consequence of the rapid sinking of the rock- 

 salt at this point. In most of the pits on this side, the 

 upper bed of rock is met with at a depth of from thirty to 

 forty yards; yet at Barnton, a mile further to the west, and 

 on the same or a lower level, none was met with in a sink- 

 ing of one hundred and fifteen yards. 



Corresponding appearances have been observed in the 

 body of rock-salt which occurs at Moulton, between Wins- 

 ford and Norlhwich, where in two sinkings on the same 

 level, and at the distance of one hundred yards from each 

 other, the difference in the depth at which the rock was 

 found, was nearly twenty yards, a circumstance from which 

 the limitation or going off of the bed at this particular 

 point may reasonably be inferred. As nothing further, 

 however, is ascertained with respect to the extent and di- 

 rection of this particular body of rock-salt, I merely met\- 

 tion the fact to corroborate the statement given of the limi- 

 tation of the great beds at Northwich. 



Another important observation with respect to the North- 

 wich rock-salt is, that there seems to be a progressive 

 thinning of the upper bed of salt from NW to SE, or in a 

 direction nearly at right angles to the longitudinal extent of 

 the stratum. Though much uncertainty exists with re- 

 spect 



