This paper reports the results of a petrographic and geochemical study undertaken to evaluate the possibility that the polymict breccia discovered in drill core from Holleford, Ontario, is the product of meteorite impact. The breccia lies in a bowl-shaped depression on the Proterozoic (Grenville) land surface and is overlain by Paleozoic rocks. The coarse fragmental constituents have been derived from the Proterozoic rather than the Paleozoic rocks. The arenaceous fraction of the breccia exhibits a very limited variety of mineral constituents, wholly of local derivation, and grain forms which indicate little or no transportation. Clay minerals from the matrix of the breccia are typical of normal sediments. No meteoritic materials have been identified microscopically, and the Ni content of the breccia is only slightly above average for sedimentary rocks. The bowl-shaped form of the breccia, as indicated by diamond drilling and geophysical data reported by Beals, is the principal criterion favoring genesis by meteorite impact. Other data neither refute nor confirm this hypothesis.