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Kellow (Joseph). The slate trade of North Wales [England], 1868. 
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232; prices, p. 239. 
Merrill (George P.). The collection of building and ornamental stones in the U. 
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Scientific American, Supp., vol. 27, p. 10874, No. 681, 1889. 
Merrill (George P.). Stone. 
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Merrill (Frederick J. H.). Mineral resources of New York State. 
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stone in New York, by John C. Smock, revised by F. J. H. Merrill, Slate, pp. 421-423. 
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With discussion. 
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vein," Pen Argyl, and Bangor regions). 
