Abstract

Engineering investigations on the Susquehanna River in Pennsylvania, in New England, and Quebec have thrown new light on the factors controlling glacial erosion, especially glacial overdeepening, and show the importance of geologic structure and preglacial topography. Near Bingham, Maine, the ice sheet widened a northwest-southwest valley in a hard, massive, crystalline schist with rectangular jointing, but had little effect where a belt of soft slate crosses the valley. Other instances of the failure of ice to remove rock benches and deepen valleys, due to the influence of geologic structure or of preglacial topography, are described at Passamaquoddy Bay, Maine, on the Connecticut River, New Hampshire, on the Deerfield River, and at Cambridge, in Massachusetts, and on the St. Maurice River in Quebec.

The buried Wyoming Valley on the Susquehanna River strikes parallel to the direction of ice movement and contains overdeepened rock basins separated by rock ridges. The maximum over-deepening is about 150 feet. Engineering investigations show that immediately upstream from the Wyoming Valley is another buried valley which has been overdeepened continuously for 8 miles, from West Pittston to Falls, although it is generally transverse to the direction of ice movement. The influence of geologic structure and of preglacial topography upon glacial erosion are indicated.

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