Since the now-classic studies of the Engels in the late 1950s and early 1960s (Engel and Engel, 1958, 1960, 1962a, 1962b, Engel and others, 1964), the northwest Adirondack Grenville Lowlands has been cited as an example of progressive meta-morphism from the amphibolite facies in the west and southwest to granulite in the east and northeast. The Engels documented mineralogical changes along a traverse within the lowlands from Emeryville to Colton, New York: muscovite gives way to K-feldspar in pelites, and hornblende and sphene progressively are replaced by pyroxene and oxides in amphibolites. The Engels inferred temperatures of about 500 to 525 °C at Emeryville and a steady increase to about 600 to 625 °C at Colton. Although today we may not agree with the exact temperatures estimated by the Engels, the trends they pointed out are well documented and have established a firm basis for newer, more detailed studies on a local scale, which have the advantage of the results of twenty years' work in experimental petrology.
In this paper I discuss some aspects of the metamorphic phase relations and the implied metamorphic conditions of rocks from a small area at the high-grade end of the Engels' traverse.