Doug-the-mason was facing the bottom of the chimney! Now that the area above the roof line has all its stone facing, we're starting again at the bottom and heading toward the top.
Here's Bob's much more coherent explanation of why we faced the top of the chimney first instead of starting at the bottom:
The flashing or interface between the chimney and the hole in the roof that the chimney rises up through is not easy to waterproof. Rain can seep down the side of the unfinished chimney and down into the inside of the roof. When the stone facing is applied this joint/seam is overlapped so water cannot enter and will instead run off onto the surface of the roof like all well behaved rain should. And stone looks much nicer than concrete too!
Yeah, that's what I said: moisture, something something.....