The coal and the associated sedimentary rocks of the Narragansett basin are progressively metamorphosed from north to south and southwest. X-ray analysis seems to give more definite indication of rank of these high-ash high-rank coals than does chemical analysis.Both chemical analysis and X-ray analysis reveal a close correspondence between rank of coal and metamorphic grade of associated rocks. At Pawtucket, coal, judged on the basis of X-ray analysis to be anthracite, is associated with rocks of the muscovite-chlorite subfacies of the green-schist facies that contain muscovite, paragonite, and chlorite. At Ports-mouth, meta-anthracite is associated with rocks still in the muscovite-chlorite subfacies and containing muscovite, chlorite, and ilmenite. At the Cranston mine, higher-rank meta-anthracite is associated with rocks in the biotite-chlorite subfacies.

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