"A record has been made of the outliers of Basal Grit occurring on the limestone of the North Crop of the South Wales coalfield, some of which have not previously been located. The solution subsidence theory to account for their present anomalous levels when compared with the parent Grit outcrop to the south has been enlarged upon, and an attempt has been made to determine the mechanism of this subsidence whichranges in vertical extent up to a maximum of approximately 600 feet. The outliers are of economic importance since their predominant crumbly quartzose sandstones are a source of almost pure silica sand."

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