Helderberg

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The westward extension of rocks of Lower Helderberg age in New York
Samuel Gardner Williams

American Journal of Science February 1886, s3-31 (182) 139-145; DOI: https://doi.org/10.2475/ajs.s3-31.182.139
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Note on the Helderberg Formation of Bernardstown, Massachusetts, and Vernon, Vermont
James Dwight Dana

American Journal of Science November 1877, s3-14 (83) 379-387; DOI: https://doi.org/10.2475/ajs.s3-14.83.379
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On Helderberg rocks in New Hampshire
Charles Henry Hitchcock

American Journal of Science May 1874, s3-7 (41) 468-476; DOI: https://doi.org/10.2475/ajs.s3-7.41.468

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