What kind of dirt?

The soil in our backyard looks like hardpan clay? (I really don't know soil classifications). Anyway, it's bare dirt in some spots where nothing is growing, and the weeds and grass seem to grow just as well in the concrete cracks as they do in the soil. I thought I'd need to get a pickaxe to break through the surface.

So since it's been raining for 24 hours, I decided to stick a pitchfork into it and see what it looked like underneath. Surprisingly, it looks like fairly rich, black dirt - however, there's a layer of maybe 8" and then you hit some rocks. Also, most amusingly, when you break into it, even after 24 hours of rain, only a very thin layer of the dirt on top is wet. The rest is pretty dry. The water runs off the surface rather than soaking in. I've heard that if you put the leaves of some native trees in your compost, the leaves have a wax that will coat the surface of the soil, and that doesn't let the water soak in.