The Apsley Gneiss can be found at Wolfe Hill (shown in this old postcard) on Cty Rd 504 just east of Apsley. It is an interesting rock formation that shows how the rock was at one point deformed and metamorphosed under great heat and pressure during the Grenville Orogeny.
Here are some pictures of the actual gneiss where it outcrops on Cty Rd 504.
East end of outcrop-
West end of outcrop-
Some scientific background on this outcrop is given here.
This paper is difficult to read without a strong geological foundation, being even more dense than the gneiss itself; however some of the general description is informative.