The 6 pound rock is pulling the large gear in a CCW direction. It is meshed with a smaller gear behind the large ratchet wheel. The ratchet is held in place by the trigger arm or what Mr Fenerty calls a deadbeat escapement. When the ratchet is released, it moves in a CW direction and engages the large wheel and gulls and sets them in motion in a CCW direction. Eventually the momentum of the wheel stops and because the wheel is unbalanced it starts to turn in a CW direction and trips the deadbeat escapement and the whole process repeats.
The rock drops about 1/4" every time it trips the escapement and it will run for about an hour and 15 minutes with a 45" drop. It hangs above a stairway in my house. It is mesmerizing to watch but it is rather loud when the ratchet is released.
Mr Fenerty has been very generous by making the plans for the mechanism available for free. You have to do some searching on the forum portion of his site to find them. He has a 45 minute video where he explains how it works. It was a fun project and has really gotten me interested in clocks and escapements.