I have to admit that I didn't look at the Gazeteer before going up there. It was only later, when uploading the pictures, that I had a quick look at the Foel entry, in preparation for anotation.
Yes, I did notice an area at the NE. edge of the pit that might indicate a whim. I didn't photograph it, if only because it would have been one of those "so what?" pictures.
In that same area there is a culvert that goes under the turbine/wheel supply incline. I'm guessing that this culvert supplied the sand saws. It is built in the style of what we call a "Roman drain" and the threshold, base slab has SD, or DS inscribed into it. I'll put a couple of pictures, in awhile, into the album, although they're not very good.