My guess is a horse/mule or ox driven mill wheel. I've seen them in use in rural Spain, and those types of set-ups were pretty common.

It's a cotton compress, used to make bales of raw cotton, some of which you can see beside it, apparently smoldering.
Casey

That makes so much sense, since this picture is supposedly showing an actual plantation in the South.

Thanks so much, both of you, for your help!

Sue

And with the soldiers - Union soldiers burning the cotton to keep it from being sold? Ransacking the house and digging up the family's buried silver?

Well, that certainly makes sense. I picked up those were bales of cotton, but had no idea what they used to bale them. The thing however, is to keep in mind when you see other structures like that in old renderings, that everything from lumber saws, to sorghum presses were at one time animal driven, and they simply walk around in circles endlessly to turn the wheels and gears levers and pulleys tethered up to overhead or breast-high booms. Yeah, I am sure the soldiers looted along the way, have read diaries of soldiers during the civil war and rations weren't always forthcoming and they scrounged often, and advantaged spoils.

Now, with your lead, I've finally found some confirmatory pictures. When I googled "cotton compress," I found large machinery (usually inside a warehouse or factory-type building) that could compress cotton for an entire town. But when I searched for "cotton press," I found photos and descriptions of smaller machines, the kind that might be used on an individual farm or plantation.

Here's a cotton press from South Carolina that is now on the National Register (the description says that it was built in 1798, and mules were used to power it):

Also, see the illustration at top left in the link (I've linked it because it's easier to see details when you magnify the image).

To a Northerner, all this is very interesting!

Sue

Here is a link that might be useful: Cotton press at upper left

I suspect that with the amount of leverage supplied, it could also be human powered. A draft animal could possibly wreck the screw if unchecked. The use of a draft animal would have been for convenience only. Very likely, it was slave powered.

Interesting picture. You can see the mules hooked to the long arms, and someone riding one of the mules to act as the on-off switch.

jemdandy - it's fairly simple mechanical engineering to make a pressure-limited screw in case the mules stampede.