Abstract

The Upper Ordovician Queenston Formation is predominantly a brick red, easily erodible, fine-grained clastic sedimentary rock that is not expected to form topographic highs. Nevertheless, the Queenston, overlain by a relatively thin cover of red unconsolidated sediments derived from it, blankets two low-relief hills. Their combined presence at the top of those hills is curious; therefore, Cholowski Hill, the larger of the two, and its surroundings were studied to try to resolve that apparent contradiction. Cholowski Hill is elongated nearly north–south and overlies a similarly shaped, north–south magnetic anomaly, which is a spur off a generally north-northeast-trending magnetic high. The spatial and geometric relationships of the hill to the magnetic anomaly, a feature of the Precambrian basement, suggest that the hill resulted from repeated tectonic uplift along faults that propagated upward from the basement, though many of them show no surface expression. Two notable exceptions are the North Russell and East Ridge faults that are topographically expressed at the surface and extend along the spine of Cholowski Hill. Their presence and that of Cholowski Hill imply geologically recent uplift. Glacial erratics on, and the smooth character of, the hill imply that it had been overridden by continental ice and was an upland prior to at least the last major glacial advance. Champlain Sea sediments surrounding and encroaching on the lowest part of the hill, but absent from the higher elevations, intimate that Cholowski Hill was not completely covered by those sediments, though it is conceivable that deposited sediments were washed away. The precise age of uplift is unknown, but the characteristics of the hill suggest a Quaternary event.

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