http://www.flickr.com/search/?q=lumsdale+mill I was mistaken about the octogonal troughs being there, they're got a load of very well-made round ones, as well as some slab-built tanks in one of the lower mills. The source of the stone was on site, one of the dams was apparently originally a quarry. The site as a whole is well worth visiting, with wheelpits, tramways, a fine chimney, and other features, all in a very picturesque valley. As for an example of the octogonal ones, I'll aim to have a wander over to Cronkston Grange over the bank holiday and see if I can get a photo.
Droid - according to John Barnatt, the numbered troughs on Stanage are actually grouse feeding stations. Another feature of interest further to the south on the gritstone edge is a rock cannon, can't remember the exact location offhand but it was mentioned in the PDMHS newsletter a bit back.
Follow the horses, Johnny my laddie, follow the horses canny lad-oh!