This aqueduct was built by engineer Robert Thom between 1825 and 1827. It takes water from the reservoir below Loch Thom and delivers it to Greenock. The aqueduct follows the contours of the hills at 541 feet, completing a route of 5 miles and collecting water from streams and small reservoirs along the way. Opened in 1827, the Cut was originally known as the Shaws Water, taking its name from the Shaws Burn.
Now set within the Clyde Muirshiel Regional Park, it's lovely to follow the footpath and there are great views over the Firth of Clyde. We last walked there in October 2007 (when I took the photo above).
See also here for an interesting website.
My later photos of the Cut here