ROC 



ROC 



cipul caufe of the falt-brine fprings in this county ; and, in 

 connection with fome other circumftances, to have a great 

 (hare in caufing the vaft differences in their ftrength, in dif- 

 ferent places. See S.\l.r-Brine Springs. 



Tliis is a ftrong fort of fait, which is found ufeful for a 

 variety of domeftic purpofes, according to the different 

 manner in which it is prepared, or the difference in the fize 

 of the particles or cryftals of which it is compofed, as will 

 be more fully fhewn under the head Salt. 



Although rock-falt is found in various parts of the above 

 diftrift, there are no pits of it wrought at prefent, except 

 in the vicinity of Northwich. And part of the inferior 

 rock-falt, which is procured there, is, it is faid, ufed at 

 fome of the refineries in that neighbourhood ; and a further 

 quantity fent down the river Weaver, for the fupply of the 

 refineries at Frodfham, in the fame county, and thofe on the 

 banks of the Merfey, in Lancafhire. The purer rock-falt, 

 or that which is called in general Pruflian rock, is carried 

 by the fame conveyance to the port of Liverpool ; whencs, 

 according to the above writer, it is exported chiefly to Ire- 

 land, and the ports of the Baltic. The annual quantity of 

 rock-falt fent down the firft of the above rivers is found, on 

 the average of the laft ten years, to be 51,109 tons. But 

 in this, it is obferved, is included wb.-t is ufed at the Frodf- 

 ham and Lancafhire refineries, which may probably be about 

 one-third of the whole. And it is added, that it appears, 

 from the report of the committee of the houfe of commons, 

 appointed to inquire into the laws refpefting the fait duties, 

 printed in June 1801, that, 



1798-I 



1799 f 



1 800 3 



were exported 



f 20,162! 



i 33'9'3 f tons of rock-falt. 



(.34.939 J 



16,095! 

 22,374 > tons 

 19,663.) 



Of this quantity, 



in 1798, 

 1799, 

 1800, - - 19,663 



were fent to different ports in Ireland : the remainder was 

 principally exported to Denmark, Ruflia, Sweden, Pruflia, 

 and Germany. However, a fmall quantity went to 

 Guernfey, Jerfey, and the Weil Indies. 



This (hews, in a finking manner, the great utility and 

 advantage of this article in a manufacturing and trading 

 point of view, as well as in other ways. 



In regard to the original formation of the beds or itrata 

 of rock-falt, in this and other countries, different theories, 

 opinions, and conjectures, have been formed and propofed ; 

 but it is one of thofe geological queftions which is extremely 

 embarrafling in its nature, and very difficult in its folution. 

 Mr. Holland has, however, in the above work, ingenioufly 

 ftated feveral fuppofitions on the fubjeft, and the objections 

 to which they are expofed. It is remarked, that wherever 

 rock-falt is met with, fulphate of lime feems to be very 

 generally difcovered in mixture with the earthy ftrata above 

 it. And the writer of the " Memoire fur le Ser Marin," 

 in the 1 ith volume of the Annals of Chemiftry, it is added, 

 informs us, that this is the cafe in Poland, Tranfylvania, 

 and Hungary ; alfo, that there is commonly a layer of 

 gypfum betwixt the flrata of ftone and the bed of fait. 

 This gypfeous layer is of different colours, and is found 

 cryftallized, itriated, and mixed with marine (hells. The 

 gypfum above the beds of rock-falt in Chefhire is, in like 

 manner, found cryftallized and ftriated ; but no marine ex- 

 uviae, or organic remains, it is obferved, are ever met with 

 in any of the ftrata. Nor does gypfum accompany it, as is 

 ufual in other places, as near Cordova, in Spain, where 



rock-falt forms a mountain 500 feet in height, and three 

 miles in circumference, as noticed by Kirwan and Towni- 

 hend. Jars, the author of the " Voyages Metallurgiques," 

 who, it is afferted, has given the moft particular account 

 we have of the upper ftratum of rockfalt about Northwich, 

 remarks, that " it appears to have been depofited by layers 

 or beds of feveral colours ;" and that " thefe layers of fait 

 are in fuch a pofition, as to lead us to believe that the de- 

 pofition of it was made in waves, fimilar to thofe which are 

 formed on the fea-coaft." 



This, Mr. Holland fays, coincides with an opinion fug- 

 gefted by Mr. Stanley, a friend of his, in regard to the pro- 

 bable origin of the beds of rock-falt, now in exiltence in this 

 diftrift ; who ftates that rock-falt is there found in feveral 

 ftrata, one above the other, with intermediate beds of in- 

 durated clay, in the vallies of the Weaver, and thofe of the 

 other rivers and brooks emptying themfelves into it ; but 

 that it has never been found fo near the furface, as to be 

 above the level of the fea, or beneath any folid rock- If 

 beds of rock-falt are to be coniidered as fo many depofits of 

 fait from fea-water, we muff fuppofe thu fea, at fome former 

 period, to have occupied the vallies in this county ; and 

 that, from time to time, the communications were inter- 

 rupted between thefe vallies (then deeper than they are now) 

 and the fea. Earthquakes, or accumulations of fand in the 

 eftuaries of the Merfey and the Dee, might, it is contended, 

 have caufed the interruptions. Whenever the fea-water in 

 the vallies became feparated from the fea, the fait contained 

 in it would fubfide, by the natural procefs of evaporation. 

 This, it is fuppofed, would the more eaiily have taken place, 

 if, by any fubterraneous fermentation, the ground below 

 the water fhou'd have been heated. To account for a 

 greater accumulation of fait than the fea-water filling all the 

 loweft parts of the diftrict would contain, we muft fuppofe, 

 it is faid, that the obllruclion interpofed between the vallies 

 and the fea had been repeatedly broken down, and re- 

 newed again. Tides, unufually high, might occafionally 

 overcome the refiftance of the accumulated fand ; and if the 

 intervals between the inundations were only of fhort dura- 

 tion, a fubfidence of fait might take place, equal to the 

 formation of the thickeft ftratum of the rock-falt now ex- 

 ifting. Long intervals between the inundations would admit 

 of an accumulation of clay, and other earthy particles, over 

 the fait thus depofited ; and in this manner would be formed 

 a new bafis for another ftratum of rock-falt to repofe upon. 

 Thus, it is thought, the regular and aftonifhing exiftence of 

 the fait ftrata may be accounted for, without neceffarily 

 fuppofing them coeval with the original formation of the 

 earth : but to confirm the theory, it is fuggefted that much 

 obfervation and clofe inquiry into the natural hiftory of the 

 county would be required. 



Mr. Holland, however, juftly thinks that there are many 

 objections to the theory which fuppofes the beds of rock- 

 falt, in this diftrift, to have been formed by depofition from 

 the waters of the fea : fome of which he ftates rather for the 

 fake of promoting ducufuon and inquiry, than of affording 

 any very decided opinion on a matter of fo much doubt, 

 uncertainty, and ohfeurity. Though on making a per- 

 pendicular fedlion of tke upper bed of rock-falt, an irregular 

 ftratification, fuch as noticed by Jars, may, he fays, by 

 frequent accurate examination, be obferved, the general 

 appearance of the fides of the openings, whence the rock- 

 falt is taken, is that of a confufed and irregular red mafs ; 

 in which fome portions of fait have a greater, others a lefs, 

 proportionate admixture of earth ; while, here and there, 

 they may be feen perfe&ly pure and tranfparent. He, 

 therefore, afks, is it likely that this irregularity and confu- 



fioa 



