Here another detail shot of the mechanism and the stonework. 

A prominent detail of the construction: The lower most gearwheels were protected (from flooding?) by some sort of fenders. They seem to be of zinc coated sheet metal (may be it's more artistic license then reality), so I tried to represent that kind of surface by using a new technique copied from figure modelers: the wet-in-wet acrylic method. As basecolor I used Citadel game Color, Boltgun Metal. Then I applied very thin cloudy coats of creamy white and traces of dark and light rust. This technique allowes you to control the colors carefully.