TRIAS. 241 



lighted up with numerous candles, the subterranean halls that have been excavated 

 during the working of Rock-salt present an appearance which richly repays any 

 trouble that may have been incurred in visiting them. The Witton mine, one of 

 the largest, has been worked 330 feet below the surface, and from it, and adjacent 

 mines, upwards of 60,000 tons of Rock-salt were annually obtained ; a part of 

 this was exported, and the rest dissolved in water, and afterwards reduced to a 

 crystalline state by evaporating the solution. The houses in which salt is manu- 

 factured are known as Wych-houses — wich or zoycJi (of Saxon origin) meaning a 

 salt-house or salt-works. In the reign of Henry VI. there were 216 salt-houses 

 in Nantwich alone. ^ 



The following section at Lawton is by Mr. G. W. Ormerod : ^ — 



Soil and gypseous marls 126 feet 



Salt 4 ,, 



Indurated clay 30 ,, 



Salt 12 ,, 



Indurated clay 45 ,, 



Salt sunk into 72 ,, 



289 feet. 



In the Marston mine, near Northwich, there are two thick beds of Rock-salt ; 

 the upper or Top-rock is 85 feet, the lower or Bottom-rock is 106 feet in thick- 

 ness, and they are separated by 30 feet of indurated red clay containing strings 

 of salt. 



Pseudomorphous crystals of rock-salt occur abundantly in the Keuper sandstones 

 and marls ; these pseudomorphs are sedimentary casts, often composed of silicate 

 of protoxide of iron.'* 



Rock-salt occurs also at Middlesborough in Yorkshire, in the Keuper Marls, as 

 well as in beds considered to be Permian. (See p. 220.) 



Referring to the Cheshire district, Mr. Strahan has remarked that as a result of 

 the removal of the vast amount of rock-salt, there have ensued the most disastrous 

 surface-disturbances. " While the bi^eaking-in of the old rock-pits has formed 

 funnel-shaped abysses from 50 to 150 yards across, the continual abstraction of 

 brine, and presumably of the upper part of the top-rock in solution, has led to the 

 subsidence of broad tracts of land, and their consequent flooding by river water. 

 The broad shallow lakes thus formed are known as ' flashes ' ; one at Northwich 

 occupies a space of about 100 acres." He adds that many Cheshire meres, for 

 example, those of Delamere Forest, are shallow-basins in drift-sand, and owe their 

 origin to other causes.* (See sequel.) 



Alabaster, a semi-crystalline form of gypsum (hydrated sulphate of lime) occurs 

 in abundance in some localities in the Red Marl or Gypseous marls of the Isle of 

 Axholme, East Bridgeford, Newark and Orston, Nottinghamshire ; Chellaston 

 and Aston, Derbyshire ; near Tutbury, and Fauld near Uttoxeter, in Stafford- 

 shire ; Aust, in Gloucestershire ; Droitwich, in Worcestershire ; Middlesborough, 

 in Yorkshire ; near Whitehaven, Cumberland ; Syston, in Leicestershire ; at 

 Watchet, and near Somerton, in Somersetshire. The Alabaster occurs in nodules, 

 bands, and in veins which traverse the beds in all directions ; it is of local 

 development. In colour it is sometimes milky-white, but is often clouded 

 and streaked with red from the admixture of oxide of iron. The purer and 

 variegated kinds are manufactured into ornamental articles, the common sort 

 (but that most largely worked) is converted by burning into Plaster of Paris, 

 which being largely used in forming moulds for the Staffordshire potters, the 



1 G. Mag. 1874, p. 260. See also D. T. Ansted, Geology, 1844, ii. 398; B. B. 

 Woodward, Nat. Hist. Notes, ii. 180. 



* Q. J. iv. 288. 



^ H. E. Strickland, Q. J. ix. 5 ; James Plant, G. Mag. 1S69, p. 377. 



* Geol. Cheshire, Iron and Steel Inst. 1S85 ; see also G. A. Lebour, G. Mag. 

 1885, p. 514. 



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