We live in a deceptively rocky area; so much so that there is actually a quarry a few miles down the road. There is about two inches of topsoil, two feet of Virginia red clay, and then nothing but basalt and diabase, a dense, igneous rock.
Every time I go by the place, I have to resist the urge to run over and look into that massive crater. The sheer size and depth of the hole makes you feel like it's pulling you down, down, down.
It may be lousy for growing plants and vegetables in the garden, but it's awesome for building highways, since the rock is so hard.
In fact, it's so hard that my brother in law broke his wrist trying to help me dig post holes in the yard. We tried the two-man gas powered auger, but gave up and had the man with the mini-backhoe do it.