Abstract

Morton L. Jandorf. York, Pa.—The Cambro‐Ordovician limestones of the York Valley are as a rule free from minerals of the heavy metals, but in one narrow stratum exposed about 5 meters down in a new quarry near the city the writer has recently observed small amounts of sphalerite, associated with a series of alteration products provisionally identified as greenockite (xanthochroite), smithsonite, aurichalcite and hydrozincite. Galenite appears to be entirely absent. The dolomite is siliceous, and shows occasionally thin quartz seams. Cavities in it may contain minute dolomite and quartz crystals, tufts of aurichalcite, and occasionally pyritohedral crystals of pyrite altered to limonite. Cavities with 60° angles are sometimes observed, which evidently represent the result of the dissolving away of sphalerite crystals, without any replacement.

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