This is an ancient stromatolite, one that dates back to the pre-cambrian from Glacier National Park. A stromatolite is a fossil formation made up of striations where ancient cyanobacteria left secretions that allowed sediments to collect in the mucus, and eventually form fossils there. Modern stromatolites form in much the same way. These cyanobacteria of the pre-cambrian are awesome in two respects:
1. They are the common ancestor of ALL life on earth. Everything, EVERYTHING started from these little guys just sitting there all the live long day munching on water, carbon dioxide and light and living the good life in the primordial soup billions of years ago.
2. They are responsible for the oxygenation of our entire planet. All of that photosynthesizing is what provided all of the oxygen in our atmosphere, which resulted in the cambrian explosion that would get the earth moving towards complex organisms. Thanks cyanobacteria!
Unfortunately because more complex creatures will tend to eat the mats of bacteria, these sort of organisms are more rare now. We don't have concrete biological evidence that the stromatolites from that period were also biologically produced by the cyanobacteria that created our oxygen rich atmosphere 3.5 billion years ago, but do have the biological evidence of the creation of ones from 2.8 billion years ago. The structure and appearance of the stromatolites from those two eras are just about identical, and so Occam's razor says that those from the earlier period can confirm these theories about conditions on early Earth. Feel free to read more, as it's always so interesting to see how unusual and "boring" fossils have told us so much about how our planet and all life on earth was formed!
Heh, I've always said I want to eventually buy a piece of ancient stromatolite and mount it in a frame with a little placard that says "Our Ancestors" on it or something, and put it up with the rest of the family photos just for perspective. :3