PRELIMINARY BEDROCK MAP OF THE MOOSE RIVER FROM MCKEEVER TO LYONS FALLS, WESTERN ADIRONDACKS, NEW YORK

The Moose River drains a portion of the western Adirondack region and is unusual because of its steep gradient over the last 25 kilometers. Erosion along this stretch of the river has resulted in abundant exposure of Middle Proterozoic meta-igneous and meta-sedimentary rocks. It is inferred that the rocks were metamorphosed and deformed during the Ottawan phase of the Grenville Orogenic Cycle.

The most abundant rock type is metagranite, but large exposures of migmatite, two–pyroxene amphibolite, quartzite, feldspar-quartz-biotite gneiss, and calc-silicate gneiss occur as well. Small, but mappable, units of marble and metapelite have also been identified.

The aforementioned units generally strike NE-SW and dip moderately NW, but local variations can be significant. In the area between Froth Hole and the old Moose River tannery, a gently plunging and gently dipping antiform / synform pair preserving quartzite, amphibolite, and Mg- & B-rich metapelite, units, is found. These units could have been part of a rift sequence prior to Ottawan deformation and metamorphism.

Other geologic points of interest in the area include post-Grenville hydrothermal quartz veins and vugs, an area of intense epidotization, local development of rose-colored quartz in quartzite units, garnet- and cordierite-rich metapelitic layers in quartzite, hydrothermal jasper-bearing veinlets, and calc-silicate and diopsidite xenoliths in metagranite.