This soil...

[Dakota Kid]

I live in Erie Pa and we have tons of shale here 90% of all the rocks are shale. Most of the lake front is cliff face ranging from 20' to 100+'. Occasionally there are mud slides down the cliff that consist of the purest clay I've ever seen in nature. I think it happens when ground water is forced out between the layers of shale, taking the shale dust with it. I'll bring my camera next time I go beach combing and see if I can find one. We used to make our own clay targets with it. They weren't fliers, but they sure were fun to plink with the .22.

[Badger]

  My neighborhood was a clay mine for many years. We have clay soil for many feet down. They would mine out a big hole maybe 2 acres or so and then lay in gas pipes and turn the whole thing into a giant oven to bake the bricks. It would take a few weeks for the bricks to cool down enough to be handled.