Blue-green algae grow on water-covered carbonate bedrock in the Bonnechere River 2 miles (3.2 km) northwest of Eganville, Renfrew County, Ontario. The algal growth is sunlight-controlled, and the growth patterns are photographic records of present-day solar radiation at the field site. Equivalent patterns may be identifiable in ancient rocks, and if so, could be used to determine paleodirections, and possibly paleolatitudes as well.

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