They were carried all the way down Changjiang river, prob from tibet where the river is started......... water polished away the outside of the agate, and at downstream where the water flow slows down, and where the river makes a big turn, one can find these pebbles. Well that held true for 10 years ago, they are so popular now that it's hard to find them on ground surface anymore, local peasants follow excavators on construction sites with bamboo baskets to pick them up and sell by kilo nowadays...