Tuesday, June 15, 2010  
   Volume 80 - Issue 24 Website:www.passherald.ca   email: passherald@shaw.ca   $1.00   
Return to Home Page

 

 
       
       
       
       
       
Quote of the Week
“Were it not for their tireless commitment to my constituents and my portfolio, I would not have received this honour.”
- MP Ted Menzies  
- on winning “Hardest   
Working Parliamentarian”   

 

Looking Back - John KinnearI grew up playing on one and the Alberta Government is the proud owner of one.  The item of which I speak can be just about any size or shape and located almost anywhere in the world. They do, however, have one common denominator; they were brought to where they now reside by glaciers.  They are known as "glacial erratics", boulders of every size that sit in the middle of fields or perched atop other rock platforms or hilltops like some kind of contemporary artwork.
"Erratics" are definitive evidence of the power and extent of the glaciations that occurred during recent ice ages.  Back in 1837 a Swiss scientist by the name of Louis Agassiz put forth the theory of a distant age when monstrous sheets of ice stretched from the North Pole to the shores of the Mediterranean and Caspian Seas; much to the astonishment of his fellow scientists.  Conventional wisdom at the time held that the existing widespread geological trauma on earth simply verified the biblical version of the "Great Flood of Noah".  To suggest that massive ice sheets thousands of miles wide and hundreds of feet deep had spread so far from the North Pole; scooping out basins, deepening valleys and scraping their way south, must have sounded preposterous at the time.  Debate raged for many years to come but common sense finally prevailed.
Ice ages did occur and their sheets left spectacular scars on the land that they violated.  They scraped away the soil, polished and gouged the bedrock and pulverized boulders to the consistency of flour.  When they ran into rock outcrops they flowed over and around them, picking up boulders and dragging or carrying them far away from their source.   Thus we have those "How the hell did that get here?" rocks scattered along valleys and left on the top of ridges.
I mentioned earlier that I grew up playing on an erratic, a monstrous conglomerate boulder from the Cadomin formation that sits atop a hill near my present home in Coleman. It is now confined to the Mountainview Industries compound, being surrounded by chain link fence.  Conglomerate is nature’s version of concrete and this well worn specimen is about a mile away from its original source bed, not a long way for an erratic but nevertheless a boulder displaced by glaciation.  Either that or the mine fire bosses were using entirely too much black powder back then!
 Out near the town of Okotoks lies the largest and most famous erratic known, that being "The Big Rock".  I guess the farmer out next to it got tired of getting his field trampled by curious passersby so the Alberta Government  bought the land around it and the Frank Slide Interpretive Centre was put in charge of it.  I guess they figured if they can look after 93 million tons of limestone, one more boulder couldn't hurt. 
The Okotoks Rock is an enormous block of grey to pink pebbly quartzite (sandstone) weighing 18,000 tons and measures 135 feet by 60 feet by 30 feet.
 
It found its way south of Calgary via a fast flowing mountain glacier in the Athabasca River valley between 13,000 and 10,000 years ago.  It was deposited onto the glacier along with thousands of other pieces as debris from rockslides and was carried eastward until the glacier ran into the Laurentide ice sheet which deflected the glacier to the southeast parallel to the mountain front.  When the ice melted a string of erratics were left in a narrow 580 kilometer belt extending from Jasper National Park along the foothills to Northern Montana. This group of boulders are known as the "Foothills Erratics Train" and "Big Rock" is the largest of them.  This erratic train documents the last and apparently only coalescence of glaciers originating in the Rocky Mountains with the southwest margin of an ice sheet that mantled much of the North American continent.
The first geologist to view and report on these particular erratics was Dr. James Hector with the Palliser Expedition of 1858-1860.  Hector misidentified Big Rock as being granite.  Of course this phenomenon did not escape the mapping eye of the renowned GSC geologist Dr. George Mercer Dawson who in the 1880’s suggested their origin was along the western edge of the Canadian Shield, hundreds of kilometres to the northeast. It was not often Dawson missed his mark but sixty years later Dr. Archie Stalker revisited this hypothesis and was able to demonstrate a source for the erratics within the Rocky Mountains.
 I recently found a smaller example of the Foothills Train in a farmer’s field on the paved shortcut that runs from Longview into High River. They call this road the Old Coal Trail and the specimen there has a deep trough worn around it and was probably a buffalo wallow for centuries.  
I've heard of a granite erratic out by Hanna, Alberta that the buffalo apparently polished to a marble finish by rubbing against it.  Granite comes from the Precambrian formation and is just about as hard a rock as you'll find, so we’re talkin' a lot of itchy buffalo for a lot of years.
I queried that respected naturalist David McIntyre about the subject and was surprised to learn that there is a line of Crowsnest volcanic boulders that “marched” eastward down the Crowsnest River valley out onto the prairie.  David in fact indentified a large boulder on a ranch near the Montana border as being a piece of the said volcanic. 
Erratics are out there in the damdest places along the foothills.  Argillite, Purcell Lava, Crowsnest Volcanics , quartzite, limestone and Precambrian boulders transported eastward and southward by  a stream of Rocky Mountain glaciers during what is referred to as the Late Wisconsinian Glaciation.  What at marvel it would have been to be able to see the magnificent icy hand of nature reach across the land is such depth and breadth, carrying with it this amazing collection of mineral jewellery.  
Return to Home Page

John Kinnear Archives

 
      Archives
 
   Volume 80 - Issue 24 Website:www.passherald.ca   email: passherald@shaw.ca   $1.00   
All information on this website is Copyright (c) 2010 Pass Herald Ltd. All rights reserved.
12925 20th Ave, Box 960, Blairmore, Alberta, Canada T0K 0E0
| passherald@shaw.ca
403.562.2248 | 403.562.8379 (FAX)