The acromagnetic map of central Pennsylvania, covering 1,800 square miles, is dominated by two large positive anomalies which apparently originate within the deep-lying crystalline rocks Minor magnetic irregularities also occur, and these are attributed to shallower sources.

In the comparatively small area under consideration, the anomalies are essentially unrelated in position and form to the sedimentary structures which trend northeast-southwest. Their probable causes are discussed and estimates of their depth of origin are made.

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