Here's a suggestion: during the battles between the Storm Tribe and the Water Tribe Helamakt had to fight a battle where the waters tried to overwhelm him. As he slew the attackers he piled their bodies higher and higher so he had somewhere to stand where he could still breathe. Eventually he built a mound high enough and had slain enough foes to win the fight. The bodies of his briny foes turned into limestone (of the coquina variety (you can still see smaller chunks of some of the deep sea monsters in the rock)).
Later on Sesarto the Artist came along and struck by the rugged beauty of the spot built Whitewall. During the construction he somehow turned the limestone into a magical marble.
Oliver
Powered by hypermail