The Earth Seal: Stone Shield ability is a defensive ability. Seal and Gate abilities are similar in the fact that they both have a drastic cost and are the same element, however, they differ in the fact that the Seal abilities are completely support abilities (except for one) and that the Gate abilities are completely offensive abilities.
The Earth Seal: Stone Shield ability creates a shield made of stone. I know it sounds weak, but here's the thing. The shield is completely unbreakable and it is very large, forming a half-circle around the user. While it is meant as means of defense, with enough speed and strength, the ability can be a defensive/offensive technique. In addition to this, the shield also is lighter than it appears, being only heavier than a shield made of stainless steel. However, the cost of using this technique is that afterwords all of the users defensive abilities will be disabled for up to 10 minutes. The technique itself will only last about 5 minutes, then the shield will crumble. The only time this technique is useless is if someone is nowhere near the seafloor and in the sea/ocean or if someone is flying.
Methods of Learning
As with the Earth Gate, reading ancient techs of the 4 Great Civilizations is the best route to go. However, any clans with Earth-Elemental Deities may know of the technique and be able to teach it.
As with the Earth Gate: Cave-In, there shouldn't be any variants, however, similar moves may be posted here.