Small, random questions about RotE that still bother you (spoilers all RotE books)

['thul]

indeed, the bark of the trees is impervious to the river water. Unfortunately it is only so when alive and unmarred, thus it is not feasible to use it for much of anything except trees.

it is indeed a nice question about transport of memory stone. Since these beings have no idea how they moved large quantities of it, they ignored that aspect. They looked at it with a primitive view, moving it like any other stone, without any magical aid. if Elderlings can move it more easily and in larger quantities, then it only makes the project more feasible, not less so. still, it would require quite a large amount to build an artificial channel.