Friday, August 22, 2014

Northern Convergence: Vancouver Island, the last of the plan that was...

Our tour of Vancouver Island in British Columbia continued. I've spent several posts (here, here, and here) describing places we saw when we scouted the island a few days before the arrival of our students, and they were really fine places to learn geology. But our students never saw them, for a variety of reasons. Today is the last of the lost stops. The next post will be about the places we did get to see, and really, they are pretty neat as well.
We are looking at the rocks exposed on Newcastle Island near the town of Nanaimo, a port on the shoreline of the Strait of Georgia. With an important exception outlined below, I never got a particularly good picture of these sandstones, but the rocks are interesting and exceedingly important in understanding the reason for the existence of Nanaimo. These are sandstones and shales of the Nanaimo Group, a sequence around 4 kilometers thick (a bit over two miles) that was deposited in a basin that paralleled the coast of North America in Cretaceous and early Paleogene time (around the time of the extinction of the dinosaurs). The basin developed as the subduction zone pushed and flexed the crust along the edge of the continent.

The seaway was populated with a variety of marine reptiles, including mosasaurs, plesiosaurs, and giant turtles. There were sharks, fish, and coiled ammonites. The sediments were deposited by turbidity currents (underwater landslides) of the edge of coastal deltas. The most important aspect of the deltas and coastal plains is that they were covered with tropical vegetation, swamps, and coastal estuaries.

The vegetation that didn't decay away was compressed into coal, and coal was the economic heart of Nanaimo. From 1848 to as late as the 1950s, coal was mined underground, following seams that sloped towards the bay. Miles and miles of tunnels were carved, reaching depths of 180 meters (nearly 600 feet). Many of the tunnels reached below sea level, and below the docks. Miners were literally working under the bay, able to hear the boats above as they worked. For many years the coal was shipped to San Francisco.
The town of Nanaimo was not the first settlement at this location (as usual, the First Nations people get the Columbus treatment). The site was originally home to a Salish people called the Snunéymuxw, from which the name Nanaimo was derived. They built longhouses here, though little trace is left. The most enduring clue of their existence are the petroglyphs that dot the region. A number of petroglyph sites are known, the most accessible of which is preserved at Petroglyph Provincial Park on the south edge of town. That's where our scouting trip took us.
The park is not large, just a few acres, but it is a small island of wilderness in the urban environment. Given my recent hobby of photographing avian species, I was looking up when I first arrived, seeing a new bird (for me), a Spotted Towhee. I understand they live in my neighborhood, but I haven't seen them there yet.
The park has a simple layout. A trail leads past an interpretive center that has some good explanatory panels (although I noticed that the word "indians" has been scratched out; "First Nations" is the preferred term in Canada these days). It also has a number of simulated petroglyphs that can be used for rubbings, since doing them on the actual carvings can damage them (Unfortunately they face many threats, from vandalism or otherwise. Another site nearby was recently destroyed during construction work).
Beyond the interpretive site, the trail climbs to the petroglyphs themselves. Fences are in place to keep people off the artwork. In this near-rainforest environment, it's amazing that the carvings haven't been more severely eroded. We found the rock exposures covered with forest duff and moss.
I was frustrated for a moment that only a few petroglyphs were visible, but it was clear that this is part of what protects the rock art. Sweeping or brushing them would surely damage them within a short period of time. I thought I had seen only one carving, a "seawolf", or sea lion.
When I was processing the pictures this evening, I realized that there were actually two of them. The second can be seen at the bottom of the photo below.
During the actual field trip with our students, we arrived in Nanaimo very late in the day, and we had a ferry to catch. And it was raining. The class was a combined geology/archaeology class, so it would have been a good spot for both classes, but that's life on the road! As will be noted later on, the storm we were in actually caused some real problems farther east.

In the next post, we'll describe what our students actually did get to see. Despite the rain, we had a pretty good day, as it turned out.

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