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of Northumberland and Durham. In the coal-mines near 

 Afhby-de-la-Zouch, in Leicefterfhire, there are fprings ot 

 brine 245 yards below the furface ; and though thefe fprings 

 are in the centre of the ifland, they are 140 yards below the 

 level of the fea. How much deeper their fource may be, has 

 not been afcertained. 



The moil obvious hypothefis refpe&ifig the formation of 

 rock-falt is, the one which fuppofes that it was depofited from 

 the fea, or by the deficcation of fait lakes which formerly 

 covered the prefent continents. Againft this it has been 

 objefted, that the compofition of rock-falt is much more 

 pure than the contents of fea-water, which contains a 

 quantity both of muriate and fulphate of magnefia, ful- 

 phate of foda, and of fulphate of lime. Rock-falt is 

 alfo found at great heights above the prefent level of the fea. 

 Thefe objections will, in a confiderable degree, be invali- 

 dated by the confideration that whatever impurities there 

 may be in fea-water, if the procefs of evaporation go on 

 very flowly the fait will be cryttallized nearly pure. Of this 

 we have an inftance in the fpecies of fait made at Lyming- 

 ton, in Hampfhire, called/a// cat, which is gradually formed 

 in the courfe of ten or twelve days, by fpontaneous evapo- 

 ration of the liquor which drains from the common fait. 

 This fait is fo pure (though evaporated from the moll im- 

 pure part, the mother water, or refidue of fea-water), that 

 1000 parts contain only 12 of foreign impurities, or little 

 more than one per cent. Thus if the deficcation of lakes 

 or bafins filled with fait water were very gradual, as it 

 muit be, except in the vicinity of fubterranean fires, the mu- 

 riate of foda or rock-falt would be cryftallized before the 

 other falts, which being more deliquetcent might be lepa- 

 rated and warned away. In this manner the fulphate of 

 lime or gypfum, which exifts in fea-water, and accompanies 

 rock-falt, may alfo have been depofited, and being nearly in- 

 foluble would remain. 



The occurrence of rock-falt deep under the earth, or 

 high above the level of the fea, can fcarcely form an objec- 

 tion to its formation from lea-water ; for it is admitted by 

 all geologifts, and is proved by undoubted fails, that the 

 ocean once covered our prefent continents. Now by what- 

 ever procefs the dry land was raifed above the fea, whether 

 by the elevation of the former, or the depreffion ot the beds 

 of the latter, extenfive hollows and clofed vallies muft have 

 formed lakes of fait water, from which the fait might be 

 depofited by evaporation. Some of thefe vallies or hollows 

 would occur in elevated fituations. With refpect to the 

 beds of rock-falt placed under other ftrata, however diffi- 

 cult it may be to explain the formation of the fecondary 

 ftrata, the exiilence of organic remains in them prove that 

 each (Iratum was once the uppermoft part of the globe, and 

 the ftrata by which it is covered were depofited upon it in 

 fuccefiive and probably at diftant periods. Nor is the diffi- 

 culty greater with retpetl to the ftrata covering rock-falt, 

 than the ftrata covering coal and beds of coal-fhale abound- 

 ing in vegetable impreffions. No organic remains have in- 

 deed been difcovered in the ftrata over the rock-falt of 

 Chefhire, but they are commonly met with at greater depths 

 over the rock-falt beds in Poland, and in other parts of 

 Europe. The occurrence of rock-falt at the fides or feet 

 of extenfive mountainous chains, may perhaps illuftrate its 

 formation, as it is probable thefe extenfive chains once 

 formed the boundaries of inland feas or lakes, when the re- 

 lative level of the ocean and our continents was very dif- 

 ferent from the prefent. 



Rock-falt is not mined in any part of our ifiand, ex- 

 cept Chefhire, though it was bored through at Droit- 

 wich ; and it exifts, in all probability, in many (if the 



weilern counties through which the red fand-rock extends. 

 We have proofs of its exiitence from the brine-fprings at 

 Droitwitch, in Worcellerfhire, at Lemington in Warwick- 

 fhire, and at Alhby Wolds, in Leicelterlhire ; and alfo in 

 the counties of Northumberland and Durham, on the eaftern 

 fide of England. The fprings at Droitwitch furnifh a brine 

 as ftrong as thofe of Chefhire. A defcription of the rock- 

 falt of Chefhire being given as an articleof rural economy, 

 we fhall proceed to give a fhort account of the molt im- 

 portant repoiitories of this ufeful mineral in other parts of 

 the world. 



Salt is very abundant in Africa ; all the plains and fandy 

 defarts are impregnated with fait, and the greater part of 

 the fprings in thefe defarts are fo faline, that it is not poffi- 

 ble to drink the water. To the fouth of Abyffinia, at the 

 feet of the mountains which feparate that country from that 

 of the Gallas negroes, fait exilts in dry and folid maffes. 

 The fummit of the mountains which border the defart to 

 the weit of Cairo, prefents an immenfe plain covered with a 

 mafs of fait. According to Horneman it is fpread over fo 

 large a track of furface, that no eye can reach its termination 

 in one direction ; its breadth extends feveral miles. To the 

 welt ol the defart ot Sahara are the great fait rocks of 

 Tegaza, on the louth-eail frontier of the defart of Zuen- 

 ziga, a little diftance from Cape Blanc. They are worked 

 by the Moors. Thefe fait mines furnifh the white and co- 

 loured fait, which is carried by caravans to Cafnah and 

 Tombuftoo, to fupply the Negro llates ; for it does not 

 appear that there are any fait mines in Negro land properly 

 called. The mines of fait fpread in that part of Africa 

 which the ancients, called Libya, have been well indicated by- 

 Herodotus, and it is in this country that he has defcribed 

 buildings conitrudled of rock-falt, like thofe in Caramania 

 and Arabia. Other fait mines, according- to Park, are 

 found on the fouthern frontier of the great defart Sahara. 

 Their produce is alfo lold to the Negroes on the borders of 

 the Niger and the Jolibe. In the kingdom of Tunis, mount 

 Had Delfa is entirely compofed of very compadt fait of a 

 red and violet colour. The lake des Marques, and the plains 

 near it, alio contain much fait. There are mines of rock- 

 falt in the country of Bamba, in the kingdom of Congo. 

 On all the weilern coalt of Africa there are fait lakes and 

 marfhes. In the neighbourhood of the Cape of Good Hope. 

 and in Caffraria, rock-falt is lets common ; but there are 

 ialt lakes to the eatt of the Cape, on the frontiers of Caf- 

 fraria, which contain at the bottom beds of fait varioufly 

 coloured. 



Salt lakes exift in the Cape Verde iflands, and natural 

 falt-marfhes, particularly in Bona Villa. 



Spain is the only country in the fouth of Europe which 

 contains extenfive repofitories of rock-falt in confiderable 

 maffes above the furface. It is found therein elevated fitua- 

 tions, forming entire hills : brine-fprings alfo iffue from the 

 feet of the mountains which traverfe that country. Ac- 

 cording to the defcription of Mr. Bowles, the repofitory of 

 rock-falt which lies between Caparofo and the river Ebro, 

 is in a chain of hills which extend from eall to weft. Thefe 

 hills are compofed of lirr.e-ftone, mingled with gypfum, the 

 chain extending "more than two leagues. In the moft ele- 

 vated part is lituated the village of Valtierra, on a flope 

 towards the middle of which is found a bed of rock-falt. It 

 may be about 400 paces long, and 80 wide. The fait is 

 contained in a bed of about five feet in thicknefs. 



" I examined," he adds, " with attention thofe beds of 

 fait ; I compared them with the layers of earth and gypfum 

 in which it is imbedded ; I found the outfide layer to be com- 

 pofed of gypfum ; and, immediately afterwards, I met with 



two 



