Haro I had to go digging for info on these puddingstone rocks after you posted about them.
Here is what I found for those w/ a need to know:
PuddingStones
The Michigan Puddingstone is a conglomerate of primarily quartzite and pebbles of jasper. The pudding stone pebbles vary in color from red to brown and pink to purple. Pudding stones are considered metamorphic and sedimentary. Pudding stone minerals contained within the rock may also vary. In some puddingstones minerals such as chromites, corundum, platinum, diamonds, gold, sapphire, and zircon have been found. Tightly cemented puddingstones make great ornamental stones when cut and polished properly.
Michigan Puddingstones were formed a billion years ago in northeast Canada. Puddingstone is a type of sedimentary rock which first formed in river channels. During the Ice Age, they were pushed down through Eastern Michigan from Ontario Canada by the glaciers. 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.
Puddingstone is ideal for the hobbyist. It can be tumbled to make wonderful key chains, necklaces and other small items. The larger pieces can be cut, polished and made into book ends, lamp shades, clocks, fountains and just about anything else you can think of.
Hunt for Puddingstones in Michigan on the far Eastern End of the Upper Peninsula and the Northeast part of the Lower Peninsula. In Canada look on St. Joseph's Island and the surrounding areas.
Its name is said to derive from a resemblance to Christmas pudding.