Quanternary Sciences Institute

Monday, May 24, 1993

University of Waterloo, Waterloo, Ontario, N2L 3G1

Paul F. Karrow

Glacial erratics

Why are many of the fields around Waterloo so stony? Why are there piles of boulders along some fence lines, gathered there by farmers clearing their fields? Why do contractors encounter so many boulders when excavating for foundations?

The glaciers did it!

Between 14,000 and 23,000 years ago, the Waterloo region was covered by glacial ice tens or hundreds of metres thick. The ice sheet was so thick it flowed like tar on a hot day, or honey on a cold day (very slowly). The ice sheet flowed here all the way from central Quebec, and on the way gathered up blocks of the bedrock between there and here. There is a confused assortment of kinds of rock left wherever the glacier passed. Blocks of rock carried from elsewhere by the ice and not native to an area are called glacial erratics. Some of the erratics are distinctive and we know where the glacier picked them up. Thus, they can tell us something about glacier flow paths. Here are some examples:

Grenville marble – derived from eastern Ontario and southwestern Quebec, a larger boulder of marble was found at Sunfish Lake. Another was found while excavating for Columbia Icefields on the University of Waterloo north campus.

Whirlpool sandstone – derived from the base of the Niagara Escarpment, north of Hamilton, a large sandstone boulder was found in a gravel pit at Bridgeport and was used to mount a plaque to Sir Casimir Gzowski on Westmount Road in Kitchener.

Jasper conglomerate (puddingstone) – derived from east of Sault Ste. Marie, many boulders and cobbles of this rock have been found in the fields of Wellesley Township.

Gowganda tillite – another kind of conglomerate, and an ancient glacial deposit itself, is derived from north of Lake Huron and is found widely in the fields to the west and north of Kitchener-Waterloo.

Native copper – pure metallic copper is found in the Lake Superior area and was carried by ice from the northwest. A large block of native copper was found in a gravel pit at Woodstock and is now kept at the Royal Ontario Museum in Toronto.

The first two examples were brought here from the east by ice flowing into them out of the Lake Ontario basin, forming the Ontario ice lobe. The last three were brought here from the northwest by the Huron and Georgian Bay ice lobes. These ice lobes met at Waterloo to form an interlobate moraine – the Waterloo moraine.

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