Naturally occurring clay usually has impurities such as rocks and sand in it. There's a way to remove these by mixing the clay in suspension and draining that water off leaving the impurities behind. I started by digging a pit to receive the clay. Then dug clay from the creek bed and put it next to the pit in a pile. Water was mixed into the pile and it was allowed to sit for a while. The water/clay mixture was then drained off into the collection pit where it settled. This was done a number of times. After settling and the water seeping out, the pure clay was mixed with grog (crushed old pottery) and made into pots. The pots were fired and of good quality, making a ringing noise when flicked indicating no cracks or weakness. This method of purifying clay saves a lot of time and effort by removing the step of manually removing rocks from the clay body.