Puddingstones were formed a billion years ago in northeast Canada. A puddingstone is a type of sedimentary rock which first formed in river channels. The white is quartz sand which has cemented itself together over millions of years. Mixed with it is a combination of other pebbles and stones of various sizes, shapes and colors. Some may even contain fossils. Another name for puddingstone is quartz conglomerate, meaning sedimentary rock composed of quartz and various other minerals.