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A Journey to a New Land

First People
Multimedia Library

Dr. Michael Wilson

Geology Department, Douglas College

Foothills Erratics Train

The closure of the corridor - this argument is based upon what we refer to as the Erratics Train. The chain of large blocks, large stone erratics that were carried from the Mount Edith Cavell area in Jasper Park, outward onto the Plains by Cordilleran ice coming from the mountains. That ice met eastern ice and was deflected southward, so the actual pathway of these erratics is an extremely important document. They were the result of a landslide onto the surface of an ice mass in what is now Jasper Park. That rock was carried outward onto the Plains on the surface of the ice. So these rocks were not even being modified much by the ice itself. They were basically being carried along as if they were on a train car.

But the ice when it reached the plains got deflected - it took a right-angle turn and moved southward. And what we realize is that it bumped into the leading edge of the Laurentide, or eastern ice mass. Now that leading edge itself was moving somewhat southward in this area, so the two, side by side, flowed southward thru southern Alberta, reaching northern Montana. When the ice melted back, a whole long row of these big boulders was left behind. They are all the same in lithology, they are all quartzite boulders. They contain little bits of rose-coloured quartz in them. They are very distinctive and they can be related back to that source in Jasper National Park. So here is a document not just of the movement of ice, but it’s a document of the closure or the coalescence of two ice masses.

Using another absolute dating technique, Lionel Jackson has managed to actually show that these boulders date to the last glacial maximum around 15,000 years ago. He’s using cosmogenic chlorine dating - these boulders are exposed to the sun, they are exposed to bombardment by cosmic rays, so the exposed surfaces are being modified over time whereas the hidden surfaces are not being modified. And when you look at the difference between the two you get an impression of how long those boulders have been bombarded by solar particles. It works really quite well and we know that these boulders date to the last glaciation.