Below the grinding wheels were a large hopper that was level with a covered gangway below it - logic would suggest a conveyor ran through this to feed the crushed raw material to the buildings below.
By Keith Miller: Excuse my ignorance on process, but I wonder if this pug mill was for crushing coal to fuel the 2 furnaces, or maybe for crusing ore for the older ironworking or even for breaking up the clay for the later brickworking?