chances are, these are fossil corals or some other reef buidler .The rock had been broken off its "ledge" and then tumbled in a stream or dumped around by a glacier.
We have similar stones in the upper Peninsula of Michigan, We call em "Petoskey STones" after the county in which theyre found.
Such kinds of rocks /fossis are found all over the world (usually we see them along beaches and in river beds
However, since the rock is quartzite, it could be a bunch of quartz crystal vugs that were broken off the outcrop.
Look closely and see whether you can see a mineral like internal structure (crystals or laminae) or actual biological features like youd perhaps see in early corals.