134 Scientific Proceedings, Royal Dublin Society. 



It is uncertain, however, whether the salt beds always occur 

 in the same stratigraphical position ; and the section of the 

 Marston mine, which the author had visited, showed that there 

 are at least two thick beds of rock-salt at Northwich, having a 

 combined thickness of about 180 feet, and at Winsford of 210 

 feet. 



This section was as follows : — 



Section i^cissed through hy the. shaft of the Marston Mines, Northwich. 



thickness. 



1. Boulder Clay, ) ^^^ ^^^^ 



2. Red Marl with gypsum, J ' " ' 



3. First bed of rock-salt, . . . . 75 to 84 „ 



4. Indurated mar], . . . . .30 „ 



5. Second bed of rock-salt, . . . .96 „ 



6. Marl and shales with bands of salt, . .180 „ 



The section had not penetrated further, but the author believed 

 that the New Red Sandstone would be found at a short depth 

 underneath. 



Beds of rock-salt have been proved in other districts where 

 the Red Marl formation occurs, as at Droitwich and Stoke in 

 Worcestershire, Shirleywich in Staffordshire, Rugby in Warwick- 

 shire, Middlesborough-on-Tees (under the Lias), Southport and 

 Preesal, near Fleetwood.* The rock-salt worked at Carrickfergus, 

 discovered in 18-50, in a boring in search of coal, occurs in three 

 beds, one of which is eighty-eight feet thick, and 572 feet from the 

 surface. 



At Northwich the pumping of brine, from which the "white 

 salt " is obtained by evaporation, has been in progress for many 

 years. Mr. Dickenson, in an official report made by order of the 

 Government in 1873-f-, has shown that in consequence of the salt 

 works there are two kinds of subsidences in progress, namely, 

 those due to the falling in of old mines of salt-rock, and those due 

 to the solution of the salt-rock owing to the pumping of brine. 

 The former class are local and restricted, although one of these at 



* Mr. J. Dickenson, Trans. Geol. Soc, Manchester, Vol. XVI. Mr. Dickenson says, 

 that Budworth Mere and Pickmere are evidently on the outcrop of the top bed of salt-rock 

 and Kosthern Mere on that of the bottom bed. But on consulting the maps of the 

 Geological Survey, he ■will see that owing to a large fault marked on the map these 

 three meres occupy the same position Avith reference to the strata. 



t Report on " Salt Districts (Landslips)," by Joseph Dickenson, Inspector of Mines. 



