346 A Sketch of the Natural History of 



dral form. The lines which form the boundary of these 

 figures are composed of extremely pure white salt, forming 

 a division between the coarse red rock exterior to the figure, 

 and the equally coarse rock included within its area. These 

 bordering lines or rims vary from two to six inches in 

 width. The figures then)selves difter greatly in size ; some 

 of them beine; less than a vard in diameter, others as much 

 as three or four yards; and they very frequently are ob- 

 served, one within another, gradually diminishing in size 

 to a centre. Professor Piayfair, in his Illustralions. of the 

 Hullonian Theory, has stated, that the compression of these 

 figures is always mutual ; the flat side of one being turned 

 to the flat side of another, and never an angle to an angle, 

 nor an angle to a side. This i-emark, as far as my observa- 

 tions have gone, is perfectly founded in fact. From the 

 mode of working the mines, it is difficult to ascertain the 

 progressive appearance of these figures in a perpendicular 

 plane. It has been stated to me that their form is a pyra- 

 midal one, the area enlarging by a determinate ratio of 

 increase as they are traced downwards ; but several circum- 

 stances induce me to consider this statement as a very 

 doubtful one, and certainly founded upon insufficient evi- 

 dence. 



One very important negative fact remains to be men- 

 tioned with respect to the internal structure of the Cheshire 

 rock-salt, viz. that no organic impressions or remains have 

 ever been met with in any of the beds of the mineral which 

 have been worked in this district. This fact rests on evi- 

 dence of a satisfactory kind, and I am not aware of more 

 than a single instance adduced in opposition to it, and that 

 of a very dubious nature. The same remark may be applied 

 lo the strata of argillaceous stone between the two beds of 

 rock salt. The veins of rock-salt intersecting these inter- 

 mediate strata contain principally the fibrous variety of the 

 fossil. It may be remarked too of these strata, that at their 

 junction with the upper and lower beds of rock-salt, the 

 lints of division are nearly as distinct as that between the 

 upper bed of rock and the superincumbent layers of argil- 

 laceous stone. 



Comparative View of the Cheshire and Contimental Salt 

 Mines. 



The want of sufficient materials with respect to the his- 

 tory of the continental salt-mines prevents me from eiitering 

 into circumstances of comparison so minutely as 1 could 

 have wished j considering such comparison to afford the 



best 



