Outlines of Geology. 35 



placed with regard to the preceding, rising from under them at 

 very various angles into lofty mountain chains, skirted by the 

 red marl which occupies the extended plains at their base, u go 

 that the appearance of the whole may be described by the figure 

 of a sea composed of horizontal beds of red marl, &c, surround- 

 ing elevated islands, consisting of rocks of the coal formation or 

 carboniferous mountain limestone, old red sandstone, slate and 

 granite, all variously and irregularly stratified." 



In the red sandstone of Droitwich in Worcestershire, and at 

 Northwich in Cheshire, are our most considerable beds of salt : 

 at the former place, they are inundated, and form what are called 

 brine springs ; at the latter, the solid salt is accessible, and has 

 been excavated to a great extent both in width and depth. At 

 Droitwich, the brine contains about one-fourth its weight of salt, 

 and furnishes upwards of 10,000 tons annually. From this source 

 the revenue derives an annual duty of £320,000; a fact, notwith- 

 standing the partial advantages that accrue from it, greatly against 

 the suspension of that equitable tax. At Northwich the quantity 

 of solid salt annually raised exceeds 150,000 tons, about 16,000 

 of which are consumed at home, and 130 to 140,000 exported. 



As the Cheshire salt deposits are below the level of the sea, it 

 has been conceived that the ocean once covered the districts, and 

 there let fall these enormous masses of muriate of soda, and that 

 the clay, sandstone, and other substances, have resulted from the 

 ruin of older rocks ; but the salt is not such as would be obtained 

 by the spontaneous evaporation of sucli water as our ocean now 

 contains. Others regard these salt pits as the bottoms of large 

 cauldrons, in which sea water has been boiled down by subterra- 

 nean heat, and left the bed of salt like the earthy fur upon the 

 bottom of a tea kettle : I do not know that there is much choice 

 between either of these hypotheses. 



In describing the coal-fields of England, I can only advert very 

 generally to their arrangement and contents. The Encyclopedia 

 Britannica contains two valuable articles upon this subject, and 

 the details respecting the south-western coal-district of England, 

 published in the first volume of the second series of the Geo* 



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