Abstract

Compositional parameters are defined for till samples collected from 48 sites in the type areas of the Malone and Fort Covington tills in the St. Lawrence Valley, New York. Till compositional variations are related directly to the influence of the underlying bedrock and are interpreted as facies changes that occur within one extensive till unit. The Fort Covington-Malone drift boundary as previously mapped is disputed. The single till sheet ranges from a gray, silty sand, carbonate-rich facies where underlain by dolostone bedrock in the north to a red, sandy, carbonate-depleted facies where underlain by sandstone and Precambrian metamorphic bedrock to the south. In contrast to previous studies, till fabrics failed to distinguish units and were not useful for correlation.

Surface till in the area is correlated with the upper till exposed in St. Lawrence Seaway excavations. The name Fort Covington Till is retained but extended to include surface till in the Adirondack Highlands. The lower till exposed in the Seaway does not outcrop in the area, and the name Malone Till should no longer be used.

The surface till may represent glaciation at least throughout the late Wisconsinan. Extension of ice into the Adirondack Highlands is suggested by continuity of the till sheet and by ice flow indicators throughout the Lowlands. Major physiographic elements influenced ice movement in that ice was channeled southward through the Champlain Basin, southwesterly parallel to the St. Lawrence River into the Ontario Basin, and southward into the Adirondacks in a lesser flow strength.

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