Abstract

High River Gravels

In the survey of quadrangles bordering Susquehanna River from Harrisburg to below Columbia, Pennsylvania,3 river gravels at several levels were observed and mapped. The highest gravels were found on benches in the Hellam Hills, southwest of Marietta, Pennsylvania, at an altitude of 750 feet, 500 feet above the river, which at this point is 240 feet above sealevel. These hills are composed largely of resistant Cambrian quartzite, which also forms the quartzite cliffs at historic Chickies Rock, to the east, where the river cuts through the Hellam Hills. The preservation of these old high gravels so close to the river is due to the resistance of the quartzite to erosion. The gravel exposed in a road cut on the mountain side is composed of smooth, well-rounded pebbles and cobbles, chiefly of milky white quartz, the largest 3 inches in diameter, in‐closed in white sand and in part . . .

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