July 1997

On a 3000-mile journey through Ontario, Canada, Heather Sloan, Graham Stewart, and a crew of Museum colleagues collected many different rocks from the Huronian Supergroup. This is a group of rock formations between 1.8 and 2.2 billion years in age which include sandstones, mudstones, and glacial conglomerates. They provide evidence of geologic processes occurring during early Earth history, in the form of ripple marks, boulders of slickensides which show movement along a fault, and boulders showing the deformation associated with mountain building on conglomerates.

An outcrop of Glacial Conglomerate, a boulder of which was collected for the exhibit. Note how the layer with large clasts is above the layer with smaller clasts. This is due to quick settling. Normally, the heavier layer (with large clasts) would settle to the bottom first.

photo credit: Craig Chesek, © American Museum of Natural History