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VI.—On the Millstone Grit of the North Wales Border
Published online by Cambridge University Press: 01 May 2009
Extract
The Millstone Grit of the North Wales Border follows the eastern slope of the Carboniferous Limestone, from Crickheath and Sweeney, South of Oswestry, to the shores of the Irish Sea; it is also thrown up into the range of hills which the traveller by the Great Western Railway may see to the west of the line between Oswestry and Chester. This range serves as a natural boundary between this part of England and Wales, and forms a second line of natural fortification, strengthened on the English side by numerous outposts of low hills of clay, gravel, and sand, which give place, upon the Welsh side, to precipitous escarpments of Mountain Limestone, beyond which the change in the language, dress, and manners of the people is marked and sudden.
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1 It is difficult to account for the origin of these Pockets, and it is with diffidence that I venture to offer the following suggestion, viz.: That in the centre, where we now find the clay, there was originally a concretion of mineral matter; next, by electro-chemical agency, such as is supposed to have aided in the formation of some mineral veins, this mineral matter was disseminated around to the boundary of the present pocket, and the felspathic clay—the cementing matrix of the rock—concreted into the central cavity thus made by the dispersion of the mineral base, leaving the sand, which had become discoloured by the dispersion of the mineral matter, simply cohering by the force of the surrounding rock.