The Limestone wall will be a 3 or 4 foot high wall seperating the lower seating bowl from the football field.
On the current Bramlage structure they could put on a limestone veneer, but probably won't because of the expense, and weight issues. If look at the addition to Vanier, most of that limestone is actually a veneer over a concrete wall.
The new basketball faciilty proposed for the West side of Bramlage will have an all limestone outer wall though, or most of it will be, there's a lot of glass invovled as well around the top of the outside, to allow natural lighting into the practice court.