The Precambrian Apsley gneiss forms part of the Grenville Series, outcropping mainly in Chandos Township in southeastern Ontario. The principal member is a biotite-microcline-oligoclase-quartz rock. Its original premetamorphic nature cannot be determined by geological criteria: the most likely protoliths are silicic volcanics or sandstones.Analyses of 49 specimens are compared in various ways with large numbers of igneous and sedimentary rocks of similar ranges in bulk composition. Two-variate scatter diagrams proposed by Köhler and Raaz, by Weisbrod, and by Moine and de la Roche permit identification of sedimentary parentage in favorable cases. Discriminatory analysis is better, and the following function (wt. % values) is recommended for rocks of this kind:Positive values of DF indicate probable igneous parentage; negative values are sedimentary. Discriminant functions including trace elements cannot be adequately appraised until more data are available for ordinary sedimentary rocks.The Apsley biotite gneiss is probably a series of interstratified silicic volcanics (about 60%) and sandstones.