318 Geological Society, 



rock. It also differs from this last in containing slender 

 veins of trypsum. 



No new brine pits have been sunk for the last thirty 

 years : the onlv particulars therefore concerning the strata 

 coverino the salt, which Mr. Horner has been able to ob- 

 tain, are derived from Dr, Nash's History of Worcestershire, 

 and from an inhabitant of Droitwich who was on the 

 spot when the last pit was sunk. From these authorities it 

 appears that the depth of from 35 to 45 feet below the sur- 

 face is occupied by beds of gravel, of red marly clay, and 

 of blue and white stone. To these succeeds a bed of gyp- 

 sum about 105 feet in thickness, immediately below 

 which is what is called the River of Salt ; which is a stra- 

 tum of nearly saturated brine 22 inches in depth, lying on 

 a bed of rock salt, the thickness of which is unknown, no 

 horinejs have been sunk in it to a greater depth than five or 

 six feet. In constructing the pits, the method is to sink a 

 shaft about eight feet square into tiie gypsum, and then to 

 ■pierce this ted by a borer four inches in diameter : the 

 borer is known to have passed through the gypsum by its 

 suddenly dropping 22 inches, the depth of the River of 

 Salt. As soon as the borer is withdrawn, the brine sud- 

 denly rushes up and overflows at the niouth of the pit. 



There are only four pits at present in use, and the an- 

 nual quantity of salt which they afford is about 16,000 

 tons. 



The brine from all the pits is perfectly limpid, and when 

 in a large body has a pale greenish hue similar to that of 

 sea-water. To- the taste it is intensely saline, but without 

 anv decjree of bitterness. The specific gravity differs in the 

 different pits, probably on account of the greater or less 

 accuracy with which the land springs are stopped out: 

 that of pertectly saturated brine is equal to 1210'39 (wa- 

 ter being 1000) ; that of the five pits examined by Mr. 

 Horner was found to vary from 1206-11 to 1174*71; 

 and an evaporation afforded from 2289*75 grs. to 1922' 97 

 grs. of entire salt, dried at 180^ Fahr., in a pint. 



This salt, from a careful analysis, appears to be com-» 

 posed of 



96"48 muriate of soda. 

 1-63 sulphate of lime. 

 1*82 sulphate of soda. 

 0"07 muriate of magnesia. 

 100-00 



On comparing the brine of Droitwich with that of Che- 

 shire, as described by Mr. Hollund in his Agricultural Sur- 

 vey 



