I know a few info about them. Its called illakanam (rules of how the grammer format should be) and illakiyam, (poems wrote according to that illakanam). Many such poems have been destroyed due to various reasons.
About kumari kandam, lots and lots of evidence are there in Tamil literature. Many Tamil literatures point out that Lord Murugan, killed a asura king in kumari kandam after breaking a big mountain there. Lord Muruga, son of Lord Shiva dominated southern India, the kumari kandam and is worshipped as God till now in India, Sri Lanka, Singapore and Malaysia. All literatures including Lord Muruga and also local stories about him revolves about this kumari kandam.
We can find notes of such unknown things from old literature only. For more proof more research is needed on the submerged site of kumari continent.