Precambrian Stromatalites (fossil algae). Glacier National Park
Stromatalites are some of our earliest life forms. Essentially, they are fossilized algal mats: marine plant life that could grow on the bottom of a shallow, calm ocean. It typically grows upward, as layers of sediment accumulate--and end up forming dome-shaped features within the rock. These ones, in the Helena Formation of Glacier National Park, weathered out in relief, to show what the living mats must have actually looked like! And they're more than a billion years old.

Our field geology course, which is based in SW Montana, usually takes a short field trip to Glacier Park in July --and we typically have a day off for hiking. This particular location, just below the Grinnell Glacier, must be one of the best mountain trail hikes I know. Not only are these stromatalites on spectacular display, but the hike itself is wonderful --and the Grinnell Glacier is amazing, its cirque is amazing, and the Purcell Sill, a dioritic intrusion, cuts right across the glacial headwall.

Druid Arch


See more images of stromatalites or Glacier National Park --then type "stromatalites" or "Glacier National Park". To see any of the features listed above, you can use those as keywords.
See a geologic map of Glacier National Park.

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