well, it's not really a biome. just a huge plate of ice in the ocean.
but it shouldn't appear on the shores of desserts, that's weird.about the cathedral:
unfortunately i forgot that the debug info is now hidden in 4.12.
i forgot to enable it and i didn't note it's position either ...
but if i remember correctly i started my adventure from the wooden stargate ...
Edit:
yesterday i went on a great adventure. i started with the intention to stalk wepawetmose, but didn't know that he used a teleport potion to teleport beyond 25000. after walking with a boat and winged mese boots for a long time i gave up, but then my adventure started ...

i climbed the highest mountain on Xanadu!
it is 176 nodes high (above the clouds) and it has green beans and forests of wild healing trees!
i got my own first healing tree from a secret underground farm. later i found 3 snowy mountain peaks that should have healing trees, but didn't had any. i thought that i would never see a wild healing tree, because they were all stolen. so i ventured to the mountain peaks again to plant new healing trees and restore the former beauty of the map.
i remember finding healing trees in my old singleplayer world, but i've never seen a forest like this.
at a certain height the snowy mountain biome ended and plain stone formed the peak of the mountain.
it contains very small amounts of iron and copper and even 1 diamond.
(well, not anymore. i took the diamod. :P )
since the coordinates became blurred when i scaled the image down, here is an original sized screen shot with readable coordinates:

i also encountered a snow monster. i enjoyed how it threw snowballs at me, but since it was only a single one on this huuuge field of snow it was very disappointing.
snow monsters should either spawn more frequently or be stronger.