The Foothills Erratics Train is a long, narrow ( wide), linear scatter of thousands of typically angular boulders of distinctive

quartzite Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tec ...

and pebbly quartzite that lie on the surface of a generally north-south strip of the

Canadian Prairies The Canadian Prairies (usually referred to as simply the Prairies in Canada) is a region in Western Canada. It includes the Canadian portion of the Great Plains and the Prairie Provinces, namely Alberta, Saskatchewan, and Manitoba. These provin ...

. These boulders, which are between and in length, are glacial erratics that lie upon a surficial blanket of

Late Wisconsin Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effect, ...

glacial

till image:Geschiebemergel.JPG, Closeup of glacial till. Note that the larger grains (pebbles and gravel) in the till are completely surrounded by the matrix of finer material (silt and sand), and this characteristic, known as ''matrix support'', is d ...

. The largest glacial erratic within the Foothills Erratics Train is Big Rock.Stalker, A MacS (1956)
''The erratics train, Foothills of Alberta''.
Geological Survey of Canada, Bulletin no. 37, 28 p.Stalker, A MacS (1975). ''"The big rock."'' In Structural geology of the foothills between Savanna Creek and Panther River, S.W. Alberta, Canada. May 23, 1975. H. J. Evers and J. E. Thorpe, eds., pp. 9-11. Calgary, Alberta, Canada: Canadian Society of Petroleum Geologists. The narrow strip of prairie covered by the Foothills Erratics Train extends along the eastern flanks of the

Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico ...

of Alberta and northern

Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columb ...

to the International Border. The boulders of the Foothills Erratics Train consist of pink and purple Lower Cambrian shallow marine quartzite and conglomeratic quartzite, that are not native to this region of Alberta. These rocks only occur within the

Gog Group The Gog Group is a stratigraphic unit in the Western Canada Sedimentary Basin. It is present in the western main ranges of the Canadian Rockies in Alberta and British Columbia, and in the Cariboo Mountains and in the central Purcell Mountains in ...

that is exposed in the

Tonquin Valley The Tonquin Valley is located in Jasper National Park, Alberta, Canada, next to the border of the provinces of Alberta and British Columbia, an area which is also the continental divide, running along the peaks of the South Jasper Range (includi ...

in the

of central western Alberta. Their specific source has been identified as being near

Mount Edith Cavell Mount Edith Cavell is a mountain located in the Athabasca River and Astoria River valleys of Jasper National Park, and the most prominent peak entirely within Alberta. The mountain was named in 1916 for Edith Cavell, a British nurse executed ...

Jasper National Park Jasper National Park is a national park in Alberta, Canada. It is the largest national park within Alberta's Rocky Mountains spanning . It was established as a national park in 1930 and declared a UNESCO World Heritage Site in 1984. Its locatio ...

. Lying on prairie to the east of the Rocky Mountains, the larger glacial erratics of the Foothills Erratics Train are visible for a considerable distance across the prairie and likely served as a prominent landmark for Indigenous people.Jackson, L.E. Jr., Phillips, F.M., Shimamura, K., Little, E.C., 1997. ''Cosmogenic ³⁶Cl dating of the Foothills erratics train, Alberta, Canada.'' Geology. 25:195–198.Jackson, L.E. Jr., Phillips, F.M., Little, E.C., 1999b. ''Cosmogenic ³⁶Cl dating of the maximum limit of the Laurentide Ice Sheet in southwestern Alberta.'' Canadian Journal of Earth Science. 36:1347–1356.Cruden, DM, W Langenberg, and RC Paulen (2003). ''Geology of the Frank Slide and southwestern Alberta. Edmonton Geological Society – Geological Association of Canada annual field trip celebrating the 100th anniversary of the Frank Slide Disaster.'' Edmonton, Alberta: Edmonton Geological Society. 34 pp.

Geologic history

Near the end of the Pleistocene, between 12,000 and 17,000 years ago, a massive landslide occurred within the Tonquin Valley in the Rocky Mountains of central western Alberta. This landslide deposited millions of tonnes of beige to pinkish quartzite and quartzitic conglomerate of the Gog Group onto the top of a valley glacier. This mass of quartzite and quartzitic conglomerate was carried eastward by this valley glacier. After leaving its valley within the Rocky Mountains, this valley glacier coalesced with other valley glaciers to form part of the Cordilleran Ice Sheet. The former valley glacier as part of this ice sheet collided with the

Laurentide Ice Sheet The Laurentide Ice Sheet was a massive sheet of ice that covered millions of square miles, including most of Canada and a large portion of the Northern United States, multiple times during the Quaternary glacial epochs, from 2.58 million year ...

and it and the erratics of quartzite and quartzitic conglomerate were diverted southward along the boundary between these two ice sheets. Together they flowed parallel to the eastern flanks of the Rocky Mountains as far south as northern Montana before the ice sheet stagnated and melted. As the ice sheet melted, the erratics of Gog quartzite and quartzitic conglomerate were deposited as the narrow line of rocks known as the Foothills Erratics Train.Tharin, J.C. (1969). ''The Foothills Erratics Train of Alberta, Canada.'' Michigan Academician. 2(2):113-124. As they were transported down valley and later southward, the highly fractured boulders and other landslide debris were neither broken up into smaller blocks, rounded, nor marked with glacial striations because they were carried either on top or in the upper part of the glacier as it moved. In addition, the atypically linear string of glacial erratics that comprise the Foothills Erratics Train was created by the parallel, non-turbulent flowage of two very large ice masses—the Cordilleran Ice Sheet to the west, and the Laurentide Ice Sheet to the east—that occurred at the boundary between them. Had they been transported by either ice at the bottom of the glacier; by water; or by ice-rafting, the highly fractured boulders and other rocky debris would have been either quickly broken up into much smaller fragments, significantly rounded, widely dispersed over the landscape, or some combination of these.

References

External links

* Anonymous (nda
Geology: Airdrie glacial erratic, near Calgary
Royal Alberta Museum, edmonton, Alberta, last accessed July 23, 2015. * Fortney, V. (2015)
Fortney: Condo excavation digs up glacial erratic.
Calgary Herald, March 19, 2015, last accessed July 23, 2015. * Jackson, L.E., Jr. (2010

last accessed July 23, 2015. * John, B., and Jackson, L.E., Jr. (2008
Stonehenge's Mysterious Stones: A tale of glaciers, man, rocks and North America.
Earth Magazine, American Geosciences Institute, December 31, 2008, last accessed July 24, 2015. {{Continental Glaciations Cambrian Alberta Glacial erratics of Canada Quartzite formations Cambrian System of North America Geology of Alberta