I collected a several hundred "purvington" pavers from a street project this spring. The crew has been laying the pavers this week, and we've all been wondering how the pavers became warped. The seemed to have been squished together.

Is fired clay a liquid like glass? Did the stones press together over the past 100 years to take on this new shape, or did they come out of the kiln like this?

Perhaps this happened when the temperature was raised when the street was covered in blacktop?

Anyone know the answer?