Originally posted by NiceGuy:

Why anyway would one need a surtling farm... At the point you survive the swamps surtling cores should not be a problem anymore.

It's more for the coal. Every time the spawner goes off, it gives you more than a half a stack.
We prepared two spawners that happened to be on the way to several crypts. On the last run, we grabbed 18 stacks of iron ore and all the stacks of coal we could traveling back and forth through the swamp to our outpost dock. In the end, we had enough coal to smelt all 18 stacks of iron.