ROCK-SALT BEDS. 331 2. Magnesian stone. P s .S Paleozoic, g Lime- / Red and white marls. Thin-bedded compact limestone, with very little magnesia and few organic remains. Red and white marls and gypsum. < White, yellow, or reddish magnesian limestone in thick beds, crystallised, compact, or earthy, and containing marine organic remains. Marl slate, in thin layers, occasionally < enclosing fishes. \I.Y ellow or purple (An extremely variable series of sand sand and sand- I stones, sands, and clays, of various stone and marl. < colours, irregular thickness, and much | local diversity of character. Plants \ like those of the coal-measures. Rock-Salt.—Cheshire unites with the southern part of Lanca shire and the northern part of Shropshire into a great plain, fifty miles long from north to south, and about twenty-five or thirty wide. 1 It is bounded on the east and west, and interruptedly on the south, by ranges of carboniferous hills; and the internal area is divided by two ranges of rising ground into three minor plains, which serve to con duct the Dee, the Weaver, and the Mersey to the Irish Channel. The range of Delamere Forest on the west, and an undulated tract ranging nearly westward to Halton and Runcorn, define the drainage of the Weaver, and include the most abundant sources of salt. Scarcely any rock-salt is found except in this limited tract. On approaching the estuary of the Mersey, the ridges which bound the plain approach one another at two points, and suggest the idea of the included plain hav ing been once a lake. Accumulation of Salt.—The mode of accumulation, judging from the associated materials, leads us to believe that it took place in “ ex tensive basins of deposit, subject to incursions from the sea, in which the water underwent concentration,” until its gypsum and salt were thrown down, chemically precipitated, or supersaturated. The pre valent type of sedimentation was that of open sea. The salt which lies under the Cheshire plain is found to thicken, at least partially, toward the contraction of the valley ; it does not, however, lie beneath the whole surface of the low ground, nor indeed in one connected mass, but occurs in detached flattened masses of limited area. The rock salt of Northwich ranges north-east and south west, and its breadth is about three-quarters of a mile. The upper bed is thickest on the north-west, and thins off towards the south-east Two beds of salt at Northwich, &c. Three beds at Lawton. Rock salt, 84 to 90 feet. Marl, &c., 42 yards. Parting of ) , Salt, 4 feet. marls, &c. 5 3° Teet , Marl, &c., 10 yarda Salt, 12 feet. Rock-salt, 96 to 117 feet, and more. Marl, &c., 15 yards. Salt, 24 yards. 1 Holland, Trans. Geol. Soc., vol. i first series.