Last year the author read before the Paleontological Society a paper prepared jointly with Arthur B. Cleaves on the Hamilton group of eastern Pennsylvania. A quoted summary of the results will render clearer the present interpretation of the same group in central Pennsylvania:1

“The authors have followed the Hamilton group from northern New Jersey to central Pennsylvania. Its four formations—Moscow, Ludlowville, Skaneateles, and Marcellus—can be recognized throughout except in New Jersey, where only the lower part of the group is identified, and in Perry County, where abnormal sedimentation tends to obscure boundaries. Certain subdivisions are recognized. . . .

“The base of the Hamilton group is nearly always defined by the presence of the underlying Onondaga limestone or shale. The top is less clear and is often designated on faunal rather than on lithologic data. Although the Hamilton faunas lack several common New York forms, there is hardly a new . . .

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