The world beneath our feet

Prof. Rebecca Jamieson descends into the Coburg Road crater. (Nick Pearce Photo)

Take a stroll along Coburg Road and you might just get a glimpse of the past.  To the untrained eye, the construction site on the corner of LeMarchant Street may look like nothing more than a huge hole in the ground. But the rocks tell a different story.

Upon closer inspection, you might notice bands of various colours weaving their way through the rock. Like the strata you’d find if you drilled into the sea floor of the Scotian Shelf, these layers represent just that: a slow accumulation of sediment at the bottom of the ocean. Once upon a time (about 500 million years ago, if you’re wondering), Dalhousie was underwater.

But that’s not the only thing you could learn from looking at the Coburg Road hole. If you also happen to have some geological background and a microscope, you could discover for yourself what Professor Rebecca Jamieson has uncovered during her time with the Department of Earth Sciences.

By taking samples from construction sites over the years, Prof. Jamieson has managed to piece together a geological map of the Studley campus bedrock. Prior to her investigations, hardly anything was known about the world beneath Dalhousie—it was, quite literally, “an example of finding an interesting research project right beneath your feet.”

Expecting to find nothing of particular interest, her first glimpse of Dalhousie bedrock under a microscope had a surprise in store.  Not only did the rock demonstrate the obvious layering of its sedimentary past, but another geologically significant event had once more transformed it—this time on a microscopic scale.

Essentially, molten granite had metamorphosed the rock into slate.  But, depending on where the sample was taken from, the crystals in the rock varied, indicating differences in temperature that correlated with the site’s distance from the granite.  Using this information, Professor Jamieson identified temperature lines that cross-cut the folding of the sedimentary layers.  In plain English, that means that if you head from the Tupper Building to Shirreff Hall, you’ll basically be moving from what was once a “cooler” part of the campus to a “warmer” part—and the composition of the rocks beneath your feet will change as you go.

Not one to keep an interesting find to herself, Professor Jamieson created a pamphlet in 2005 (aptly titled “Dal Rocks!!”), which provides a basic description of the geological processes revealed by the bedrock samples.  It also details the types of rocks that were used to construct Dalhousie’s older buildings, and features a campus map complete with temperature lines. In one of her classes, ERTH 3020, students have the opportunity to collect samples of their own and analyse them under a microscope.

So next time you’re heading past that gaping hole on the corner of Coburg and LeMarchant, look at it not as an eyesore – but as a piece of history that has finally seen the light of day.