One of the most fascinating features along the Bruce Trail are the crevice caves. These narrow deep canyons are formed between huge blocks of limestone along the escarpment. Occasionally, as on the Boyd property near Owen Sound, the Bruce Trail goes directly through a crevice.
The crevices only get a little light, perhaps no direct sunlight at all, so they form a cooler-than-normal microclimate. The limestone walls are covered by mosses and ferns, and sometimes liverworts. Definitely a different experience!
It is thought that crevices formed because sometimes huge fractured blocks of limestone along the escarpment slipped forward ever so slightly, on the saturated clay of the geological layer below the limestone, leaving an open crevice, anything from a few inches to several metres wide.