From Populous Wiki
Gargoyles are almost exactly the same thing as a Stone Head, Obelisk, or a Totem Pole, although they have a different shape. They are in the shape of an Angel of Death made of stone. Any shaman can worship them like a stone head, but they will usually reap better rewards than stone heads, and are much more rare.
There is special effect that can only be preformed on gargoyles, which is 'produce ending aods', which turns the statue into a real Angel of Death, then it creates two more. The middle one will head for the enemy shaman then you win the game.
Even though you can send units to worship gargoyles (and they will look like they are worshipping it), the progress bar won't rise. Only shamans can worship gargoyles successfully.