R O C 



ROC 



ture. But it continued to have this increafed degree of 

 purity for four or five yards only ; while, for fourteen yards 

 itill lower, to which depth the pit or (haft was funk, the 

 proportion of earthy matter was again as large as in the 

 upper part of the Itratum. It was therefore, on this ac- 

 count, thought ufelefs to link the pit to any greater depth. 

 Many other proprietors of pits, (hafts, or mines, in the 

 fame neighbourhood, it is (tated, followed the example 

 which had been thus fet them ; and penetrated through the 

 bed of indurated clay lying beneath the upper Itratum of 

 rock-falt. A fecond ftratum of rock-falt was conftantly 

 met with below this ; and on pafling down into it, the fame 

 order of difpofition as to purity was obferved, as in the 

 pit or mine in which it had been firft noticed and examined; 

 and the fame has been found to prevail in all the pits, (hafts, 

 works, and mines, which have iince been funk in the fame 

 vicinity. 



It is further noticed, that there is great uniformity in 

 the ftrata which are palled through in finking pits for 

 rock-falt or brine ; and that they very generally confilt of 

 clay and fulphate of lime mixed in various proportions ; 

 that of the latter fomewhat increafing as the pit, lhaft, or 

 work approaches the rock or brine. The workmen diftin- 

 guifh the clay by the appellation of metal, giving it the 

 name of red, brown, or blue metal, according to its 

 colour ; and the fulphate of lime by that of plaijicr. See 

 Quarry. 



The ftrata formed by thefe are, in general, clofe and 

 compact ; allowing very little frelh water to pafs through 

 them. In fome places, however, they are broken and 

 porous : and they admit fo much frelh water into the pit 

 or work, that whenever they have been met with, it has 

 been ufual to difcontinue any attempts to pafs through 

 thein in linking the pits. In thefe places the workmen call 

 the metal foggy. It was thought not only impracticable to 

 overcome a water, which vulgar prejudice had magnified 

 into a great Itream running under ground ; but it was be- 

 lieved, even if the finking could be continued below this, 

 that the water could not be kept out of the pit, lliaft, or 

 work, and that it would either weaken the brine fo as to 

 deftroy its value, or would find its way into the cavity of 

 any rock, pit, or mine which might be found below it. 

 Later experience, it is faid, has proved, that thefe ideas 

 were not altogether well founded. A few years ago an 

 attempt was made in Witton to pafs through this porous 

 ftratum, in order to get to the brine. It was met with 

 about twenty-eight yards from the furface ; the thicknefs 

 of it was about thirteen feet ; and the quantity of water, 

 which was forced through it into the pit or (haft, was three 

 hundred and fixty gallons a minute. By means of a (team- 

 engine, the linkers were enabled to pafs through this water; 

 to fix a gauge or curb a few yards below it, in a ftratum 

 of indurated clay ; and thence to bring up a wooden frame, 

 Supporting a wall of puddled earth twelve inches thick, by 

 which the accefs of the frelh water into the pit or lhaft 

 was in a great degree prevented, and an opportunity given 

 to pafs down to the brine below. A lhaft was afterwards 

 funk through this porous ftratum, for the purpofe of ob- 

 taining rock-falt ; which objeft was, after a fhort time, 

 defeated, by the influx of brine into the lhaft at the fur- 

 face of the upper ftratum of rock-falt ; an accident origin- 

 ating in a caufe completely diftinCt frtfm the frelh water in 

 the porous ftratum or bed. An exaft feCtion of the dif- 

 ferent ftrata funk through in reaching the fecond bed of 

 rock-falt in the pit at Witton, near Northwich, is given 

 by Mr. Holland in the above report ; and all the ftrata in 



the neighbourhood of the laft town are fuppofed to have 

 nearly a fimilar difpofition. The inclination of them in the 

 pit or (haft at the above place was from north-well to fouth- 

 eaft ; and the dip about one yard in nine. The ftratum 

 through which the trelh water flowed is {hewn, and the 

 level it found, it is faid, was fixteen yards from the furface, 

 which, it is remarked, nearly correlponds with that of the 

 brock betow. The line of feparation between the loweft 

 ftratum of earth, and the firft of rock-falt, is very exactly 

 defined; they are perfectly diitinct, and do not at all run 

 into each other. It is farther noticed, that in carrying a 

 horizontal tunnel for one hundred yards along the upper 

 ftratum of rock-falt, this was foir 1 to be irregular and 

 unequal on its furface ; the irregu n ties in a great meafure 

 correfponding with thofe on th< mrface of the ground 

 above. 



The higheft bed or body of rock-falt in the pits near 

 Northwich is the thickeft in thofe fituated the molt to the 

 north-eaft, gradually declining in thicknefs towards the 

 iouth-weft, fo as to lofe one-lixth of it in the courfe oi 

 about a mile. It decreafes from about thirty yards in thofe 

 the fartheft to the north-eaft, to about twenty-five in that 

 the molt to the fouth-weft. 



A Angular appearance is remarked to prefent itfelf on 

 making a horizontal fection of the ftratum of rock-lalt in 

 the pits : on the whole of the furface made by fuch a fec- 

 tion, various figures, it is faid, may be obferved, differing 

 in form and fize, fome of them being nearly circular, others 

 approaching more to an oval form, while in many an irre- 

 gular pentagon may be traced. Some of them are not more 

 than two or three feet in diameter ; others are ten or twelve 

 feet. The lines which form the boundaries of thefe figures 

 are white, and from two to five or fix inches wide. On ex- 

 amining thefe appearances, they are found, it is faid, to be 

 owing to the rock-falt, in the white lines forming the divi- 

 fions of the figures, being perfectly pure, and tree from 

 earthy admixture. When combined with the fait, having 

 earth in various proportions mixed with it, a general effect 

 is produced, it is laid, not very diltantly refembling molaic 

 work. This difpofition is uniformly obferved, it is faid, 

 throughout the whole thicknefs ot the ftratum of rock-falt ; 

 and that in whatever part of it fuch a fedtion as the above 

 is made, fimilar appearances are met with. To what caufe 

 it has been owing that the rock-falt has been depolited in 

 this fingular manner, it is thought difficult to conceive. 

 The whole ftratum of rock-falt may, it is fuppofed, be 

 compared to a mafs of bafaltic columns ; the lines of fepa- 

 ration in each pillar being marked by the pure and trans- 

 parent white fait. Thefe appearances, it is noticed, afford 

 feveral grounds for inferences favourable to the theory of 

 the earth mentioned under the head rock-falt, to the illultra- 

 tor of it. See Rock-<W/. 



It is likewife further obferved, that the diviiion betwixt 

 the lower portion of the upper bed of rock-falt, and the 

 indurated clay or ltone beneath it, in pits of this kind, is 

 as exafctly defined, as that between the upper portion of it 

 and the earth above. That in palling through this flone 

 fmall veins of rock-falt are met with, here and there run- 

 ning in it, in various directions ; and that wherever there 

 has been any little crevice in it, it is found filled up with 

 rock-falt, to which the clay and oxyd of iron have given a 

 deep red tinge. The thicknefs of this itratum ot ltone 

 is faid to be uniformly found to be from ten to eleven 

 vards ; and the lower part of it is as diftinct from the 

 fecond bed of rock-falt, as its upper part is from the firft : 

 alfo that its termination is equally abrupt or fudden. 



9 And 



