Seismic ravines

These would at first look like a normal ravine, but, every now and then, if you are within 30 blocks of it, you would get a potion effect called jitter, it would shake your screen and your character. These ravines would also be a source of gneiss, a rare rock that could be used to make a pressure table, putting in a partially broken item and lava as fuel  would regenerate the partially broken tool. Gneiss could also be used to make the seismic potion, a potion that gives you and other entities the jitter effect.