On the subject of hard ground and nutrient-rich topsoils,,, "Round these here parts" if you dig from 8 to 16 inches down, you are almost guaranteed of finding a nice 150 to 500 lb slab, block or boulder of sandstone. (Sort of easy to bust with a pick-axe or spike maul, just a pain is all.) So I've opted to go the overkill route, clearing the larger rocks down to the 3' mark. Theres lots of clay (Which I just happen to be using in the construction of a small refractory furnace), but theres also quite a few veins of this thick, rich, mulch-like soil (I'm guessing a combo of older root-material mixed with what looks to be decaying leaves and bark with some sand)
Now the top layer does get fairly hard when dry, but since I've washed about 200 lbs of raw clay, I have an abundance of Sand on hand which I'd guess when mixed with this mulchy-soil from around and under the larger rocks would do well as a "home-made" potting soil as I'd have to guess the mulch was loaded with nutrients and minerals. So could someone turn my guess into a know or a "No"?