Henry Holland

“ Though the evidence on the subject is not entirely of a positive nature, there seem strong grounds for believing that the beds of rock-salt at Northwich are perfectly distinct from any others in the salt district, forming what the Germans would call ligende stocke, lying bodies or masses of the mineral. It will readily be conceived that there is much difficulty in acquiring precise information with respect to the extent and limitation of these great masses, and that there are many sources of error to which such an inquiry is liable. ”

“ I have dwelt thus minutely upon local facts from their connection with the situation of the rock-salt, which, with few exceptions, has yet been ascertained to exist only in the vallies of the Weaver and its tributary streams; in some places manifesting its presence by springs impregnated with salt; in other places being known by mines actually carried down into the substance of the strata. A reference to the map will shew the several situations where brine springs occur, or where mines have been sunk, in the course of these vallies. ”

“ The methods employed in working out the rock-salt offer nothing worthy of notice. The operation of blasting is applied to the separation of large masses from the body of the rock, and these are afterwards broken down by the mechanical implements in common use. The present number of mines is eleven or twelve, from which there are raised, on an annual average, fifty or sixty thousand tons of rock-salt. The greater part of this quantity is exported to Ireland and the Baltic: the remainder is employed in the Cheshire district in the manufacture of white salt by solution and subsequent evaporation. ”

“ In Hungary and Poland these beds do not present a thickness of more than one or two feet, and are separated by layers of clay a few inches in thickness. Much, however, it is evident, must depend upon the number of the beds thus disposed, but this I do not find any where noticed. The earthy saline contents of the foreign rock-salt very exactly resemble those of the Cheshire; the gypsum existing in much larger proportion than the other earthy salts, and appearing in considerable masses, both distinctly, and in mixture with the beds of clay. ”

“ The marl beds form the most peculiar feature in the alluvial strata of the Cheshire plain. These occur in great abundance in every part of the district; being found not only under the common soil, but occasionally, as on the borders of Delamere Forest, interposed between layers of sandstone rock. The Cheshire marls are also very frequently met with in large detached masses, twenty or thirty feet in thickness, in the working out of which, it is not unusual to find large assemblages of fragments of the older rocks. ”

“ This general idea of the formation of the Cheshire rock-salt derives confirmation from the fact that, with the exception of the sulphate of magnesia, the same earthy salts occur together with the muriate of soda in these strata, as are met with in the waters of the sea. The circumstance of the beds decreasing in thickness as they recede from the sea, may perhaps be admitted as another argument in behalf of the opinion. ”

“ In every part, however, of this compound rock, we find separate crystalline concretions of muriate of soda, variously disposed, sometimes occurring distinctly in the cubical form; in other places in masses of larger size, and irregularly shaped. The colour of these concretions, which are of the foliated species of fossil salt, is usually a greyish or milk-white; they are always translucent, and often attain a considerable degree of transparency. It would appear that they contain the muriate of soda in its purest form ”

“ It would appear that the great beds of rock-salt at Northwich assume a general longitudinal direction from north-east to south-west, the line which has been traced upon them in this direction being a mile and a half in length, and no direct evidence existing that they may not extend further in these points; while their transverse extent, as measured by a line at right angles to the former, is much more limited, probably not exceeding in any place one thousand three hundred or one thousand four hundred yards. ”

“ The sandstone, in a considerable part of this range, is slaty in its structure, and would seem to belong to the Independent Coal-formation of Werner, some pretty extensive beds of coal being found and worked under it. The southern boundary of the plain, which is the one approaching most nearly to the rock-salt, is irregularly formed by ridges of limestone and calcareous sandstone, leaving open some communications with the level country in the middle of Shropshire. ”

“ It is an important fact, however, that sea-shells and other marine exuviæ are found in these beds of clay and gypsum; a circumstance which, as I before stated, never occurs in the Cheshire mines. It would seem that the portion of oxide of iron combined with the clay in the substance of the English rock-salt does not exist in the mineral as found abroad, or at least in a proportion not so considerable. ”

“ The lines which form the boundary of these figures are composed of extremely pure white salt, forming a division between the coarse red rock exterior to the figure, and the equally coarse rock included within its area. These bordering lines or rims vary from two to six inches in width. The figures themselves differ greatly in size; some of them being less than a yard in diameter, others as much as three or four yards ; and they very frequently are observed, one within another, gradually diminishing in size to a centre. ”

“ Professor Playfair, in his Illustrations of the Huttonian Theory, has stated, that the compression of these figures is always mutual; the flat side of one being turned to the flat side of another, and never an angle to an angle, nor an angle to a side. ”

“ This term will not appear too strong, when it is mentioned that in the mine from which the section of strata was taken, and where the shaggy metal was found at the depth of twenty-six yards, the quantity of water, ascertained to issue from its pores in one minute, was not less than three hundred and sixty gallons; a circumstance greatly enhancing the difficulties of passing a shaft down to the body of rock-salt. ”

“ The area of this plain may be regarded as extending nearly fifty miles from north to south, and as having an average breadth of twenty-five or thirty miles. Its eastern boundary, as more immediately regards the County of Chester, is a high range of sandstone hills, stretching from north to south along the borders of Derbyshire and Staffordshire; connected on the north with the hills in the West Riding of York, and on their eastern side passing into the limestone hills of Derbyshire. ”

“ On this surface may be traced various figures, more or less distinctly marked, and differing considerably in the forms which they assume; some appearing nearly circular, others perfectly pentagonal, and others again having an irregular polyhedral form. ”