Mining
Prospecting, shafts, levels and getting the rock home.
Find a good spot by prospecting, then sink a shaft on flat, dry ground. Each level down needs a higher Mining level and 3 logs for ladders. A full pack is too heavy to climb out with, so fit a windlass (6 logs) to wind your load up to a pile beside the shaft.
The full guide, with every level and every rock, is on the Minerals page.