That appears to be some seriously dense clay soils there, easiest to see in RM's second photo in the post above where what's been scooped out is still holding the contours of the shovel. I only mention that as—AFAIK—we don't see that consistency of earth excavated here that often. Clay pits in Toronto often ended up as locations for brick works, the best know of which are the Don Valley Brick Works of course. No idea how large a deposit is required to make a brick works viable, nor how much tolerance there is for varying compositions of clay materials that they would run into in various locations… and no idea if there was ever a minor brick works here. Anyway, I assume it won't be much further down before they hit the Dundas shale, but anyone with a more thorough knowledge of what underlies Toronto have anything that they can add?