A Story Of Stones At Old Baldy
Bend over.
More.
Even more.
You may have to
sit
on the ground
with your head
almost
touching
the earth.
You have to look
a rock
right
in the eye.- from Everyone Needs a Rock by Byrd Baylor
I will do my best to keep this one concise, but covering 4 Ga (four billion years) in a short blog post is going to be a tough one, so please bear with me.
An Introduction
The Beaver Valley was shorn into the land through the cataclysmic pummeling of boulders and rocks propelled by massive riverine torrents spilling from the melting glaciers. Smashing their way across the newly exposed landscape which had been buried under approximately 2 km (~1.25 miles) tall walls of glacial ice, massive boulders, some carried by the ice from thousands of miles away, were being unloaded by the retreating glaciers and hurled across the landscape by epic rivers of incredibly cold meltwaters. These boulders bounced and slammed against the Georgian Bay Shale, and Manitoulin and Amabel Dolostone formations and a few other layers of bedrock before being washed out to the bottom of Georgian Bay, or settling along the valley floor. A broad river, much larger and much more fierce than the present day Beaver River, ran from valley wall to valley wall, eroding rock and depositing till picked up as the glacier repeatedly grew and lurched Southwards and ebbed and waned back Northwards over 2.5 million years of various states of glaciation. This till, carried from as far South as the Appalachian Mountain ranges to the Precambrian volcanic rock of the far North of Turtle Island, was strewn about the valley floor. The area looked like many modern mountain glacial moraines found today, full of rubble and stone, gravel and sands, with no visible life to be seen.
In time, and I mean a long time, wind blown spores of lichens and fungi along with seeds of cold hardy grasses and forbs began to colonize the rubble slowly changing the landscape from stoney valley to something akin to the present day tundra. Seeds of shrubs like willows (Salix spp.) and cottonwoods (Populus spp.) may have been first if we look to the tundra for example, growing quickly and dying back, building up a soil layer more suitable for later post-glacial successi0nal species. A couple of those species were White Pines (Pinus strobus) and Eastern Hemlock (Tsuga candensis) both lightweight wind blown tree species hailing from glacial refugium in Southern Appalachia. Maples (Acer spp.) migrated up from the mouth of the Mississippi, yet took a bit longer than the lighter and hardier conifers. As the world warmed and more faunal visitors returned to the valley, larger seeds were spread. Animals like American Crows (Corvus brachyrhynchos) and Blue Jays (Cyanocitta cristata) would be great acorn and chestnut dispersers, spreading the heavier seeds with their scatter hoarding caching behaviours. I have no records or research, but I bet the Huron-Wendat people who occupied the lands of the Beaver River, and those who likely were there before them, also had a big role in whatever diverse plant species began to spread through the valley. Slowly, very slowly the valley would be transformed into the deep lush forests whose soils and possible seedbank so eagerly desire to reclaim the land if let be.
How Can We Know What Has Happened On The Land By Looking At What Remains?
Dolostone
Marcus sitting with the Dolostone.
An image of what Turtle Island/North America looked like 450 mya.
The photo above is of Marcus sitting against the sheer rock face at the top of Old Baldy. The stone is exposed dolostone which makes up Amabel Dolostone Formation. This dolostone is the product of the bodies of ancient animals which dwelt within the tropical Silurian sea about 450 million years ago.
Wait.. what?
Let me explain.
Dolostone is a sedimentary rock, formed from the calcium carbonate stored in the shells of some ancient brachiopods and cephalopods as well as from the carbonate-secreting algae which lived in a shallow tropical sea some 450 million years ago (mya). At this time our region of Turtle Island/North America was just below the equator and this gave lots of opportunity for ancient sea animals to flourish in the warm waters. The bodies of these animals were made up of the calcium carbonate mentioned above. These bodies which absorbed and used the calcium carbonate to create their hard shells eventually died and sunk to the bottom of the sea. Time rolls on and more and more bodies piled up. More carbonate was released into the aquatic environment Though time and pressure of oceans, through currents and more and more bodies piling up, limestone began to form. As the limestone begins to form a process of dolomitization occurs with the limestone becoming interspersed with magnesium found in the sea water. As the limestone becomes impregnated with the magnesium and the whole solution hardens, it all turns to dolostone.
This dolostone is very similar to limestone, yet with the addition of the magnesium, becomes very durable and is therefore less prone to erosion. While other layers of rock and shale may wash away after 400 million years, the dolostone remains as a remnant sign of the ancient sea beds. As near my home in Guelph, the dolostone cliffs of Old Baldy are like the fossilized dinosaur tracks through ancient creek beds in Texas - remnant traces of life from long long ago.
Glacial Erratics
Throughout the forests of Old Baldy there are many large boulders which do not conform to the dolostone bedrock which underlies everything. They just don’t match up with the rest of the rock that makes up the hill. If the hill is covered in rocks that don’t look like, or aren’t made up of the same stuff as the rest of the hill then we can understand, in tracking terminology, that these boulders are not part of the baseline of the landscape. We can then ask the questions, where are they from and how did they get there?
Some folks used to think that these massive rocks came from the great biblical floods of Noah. Wave action rocked the rocks back and forth for a while until the rocks ended up many thousands of kilometers from where they originated. In a distant sort of way they were right, but instead of water, it was ice.
The most recent glacial advance began about 95,000 years ago and during that period massive lobes of ice advanced Southwards across Turtle Island/North American swallowing and consuming almost everything in their path. As the glaciers covered the landscape, blocks of rock were torn off their home landscapes and carried by the glaciers only to be deposited someplace new. These rocks are called glacial erratics as they are wanderers (errare means ‘wander’ in Latin) across the land. They’re picked up, tossed around and left behind like I do with small sticks and stones on my own wanders. Now the cool thing about these erratics to a tracker might be that if geologists can figure out where the rocks have come from, then they can use these rocks to reconstruct and understand the path that the glaciers took.
I am still new to rock identification and when Alexis and I spoke about the boulder in the photo above, we both knew who to ask for more information: Bill the Bear, retired hydrogeologist and always curious and friendly tracker. I ended up writing him an email and asking what he could tell from looking at a photo of the rock. Turns out he could see a lot.
First he could tell by the colour and texture of the rock that it was likely volcanic in origin and because of that “very very far from ‘home’ ”. He wrote that it was likely composed of iron and magnesium that have been altered by chlorite on the rocks surface as result of being exposed to water over millions and millions of years. He suggested that if his assumptions were correct, then this erratic was likely of Precambrian origin. This would have been “part of the 'mountain-building' process, in what is now northern Ontario, which made the Himalayan mountains look like foothills!”
Bill mentioned Precambrian in origin which I think implies that this rock is from the Canadian Shield which is Precambrian igneous rock, which means it was formed between 3.1 Ga (3.1 billion) to the beginning of the Cambrian Period, about 538.8 million years ago. This is a massive span of time, inconceivable to me really, but somehow still awe inspiring. The word igneous means that this rock was “born of fire” or as Bill mentioned, volcanic in origin.
Rocks of volcanic origin are produced in a variety different ways. In the book Ontario Rocks by Nick Eyles, the author states that igneous rocks are formed when magma cools and becomes solid. The grain size of the the rock depends on how fast the rocks cool, with finer grains showing up in rocks that have cooled quickly and course grain in magma that has cooled slowly. This rock was rough to the touch and in my follow up research gets me thinking of a type of rock known as gabbro which is a slow cooling rock formed from molten magma from deep within the Earth’s crust. I have read that these rocks would have become solid more 1 Ga (1,000,000,000, one billion) years ago, and was eventually brought to the Earths’ surface by uplift caused by tectonic shifts and erosion caused by weather, water and wear on the land. Then again the glaciers picked it up and plopped it down at Old Baldy perhaps around 12,000 years ago.
I havn’t been able to figure out more about this rock in particular but I am in search of anything more that might flesh out the details a little more. This might take some time, but I guess that’s what this is all about. The rocks will wait.
Post Glacial Isostatic Adjustment
As mentioned above, the ice sheets around the area of Old Baldy was covered in these massive mounds ice approximately 2km thick. 2000m. 4 CN Towers. 11 Seattle Space Needles. They were @#&$*+!! huge! It’s hard to imagine how tall they must have been, let alone how much they weighed. But they weighed a lot. According to one source, a cubic meter of ice weighs about 916 kilograms (2020 pounds), so it’s kind of interesting to think of what 2000 m of ice might weigh, but really that’s just one spot. Imagine these ice sheets covering all of the Northern parts of Turtle Island/North America and almost the entirety of Canada. To quote Wallace Shawn’s character Vizzini in the 1987 hit The Princess Bride, “Inconceivable!” I can’t find actual numbers but lots of adjectives are thrown around, such as “enormous,” or “massive,” and “incalculable” are a couple of good ones. The glaciers weighed so much that they depressed the Earth’s crust and mantle below. In Northern Ontario near Hudson’s Bay there are estimates that the land was pushed down about 270-280 m (~300 yards), though less in Southern Ontario. This made the land adjacent to these depressions rise as well, like a crest or plate when considering pressure releases in animal tracking.
The rate of rebound in the area around Old Baldy in Southern Ontario would be about 4 mm per year. Image from Crustal motion and deformation monitoring of the Canadian landmass by Joseph A. Henton, Michael R. Craymer, Rémi Ferland, Herb Dragert, Stéphane Mazzotti, Donald L. Forbes. Geomatica, 2006.
But something amazing happened as the glaciers started to retreat. The land which had been previously depressed by the incredible weight began to rebound and rise up, and much the adjacent lands which had lifted began to subside (sink down again). This process of rebounding land is called Post-Glacial Isostatic Adjustment. Though it has had many other names over the years such as glacial rebounding, isostatic rebound or crustal rebound, post-glacial isostatic adjustment makes the most sense in that the land isn’t just lifting up again. Some land is subsiding (sinking), some land is being pushed away from where it once was, and this is causing changing sea levels, and even shifting the Earth’s rotation. Post-glacial isostatic adjustment translates to “Changes in equilibrium of the Earth’s crust after the glaciers” which is a more honest and accurate interpretation of what the names are trying to describe. To get back to the point, through these changes of the elevation of the land in the Old Baldy/Blue Mountains area, the land in that area has risen over 15 m since glaciation and is still continuing to rise at a rate of about 15 cm per hundred years or 1.5 cm per decade. It’s not that much in the grand scheme of things, but I still think it’s pretty wild.
When researching geology in the context of tracking the landscape I am reminded of a phrase that Alexis Burnett often attributes to one of his teachers Tom Brown Jr., and I hope I am not misquoting here.. “The Earth longs to be flat, everything else is a track.” A mountain is the track of tectonic plates shifting and smashing into one another, an odd stone in a field the sign of a glacier, and an Oak (Quercus sp.) tree is the remnant sign of a seed possibly dropped by a Blue Jay many years before.
I’ve been thinking about how in a world of calamity and upheaval, extinction and war, that sometimes there is a grounding in remembering the ancient body that we all come from.
Researching and working towards a deeper understanding of the geology of this venerated hill has actually been a peaceful reflection when places of peace have been so hard to find. I recognize that these are epic cataclysmic histories, but the stories held in the stones at Old Baldy have brought about a deep sense of peace for me when it seems so lacking in the world right now. Maybe it’s the disconnect of me not being present for the upheaval and torrent of glacial meltwaters and crushing sheets of ice, but doing the research, piecing together clues, and imagining the magnitude does create a profound sense of wonder and awe, a stupefying amazement in the unveiling of a billion years of mystery written on the body of the hill. I deeply appreciate the work and practice of listening to the stones and tracking the beauty of the land.
To learn more :
Walking Through Time : Exploring Niagara Escarpment Geology in the Beaver Valley Bruce Trail Section by Beth Gilhespy, M.Sc. Self published, 2023.
After The Ice Age : The Return of Life to Glaciated North America by E. C. Pielou. The University of Chicago Press, 1991.
Ontario Rocks by Nick Eyles. Fitzhenry & Whiteside, 2002.
Geology and Landuse Between Guelph and Hamilton: A Self-guided Tour by Chesworth, W., Martini, P., McCarthy, P. and Sadura, S. Dept. Land Resource Science, University of Guelph, 1996.
Ancient Earth interactive globe - see what the Earth looked like from 750,000,000 years ago up to now
NASA’s video on Earth Rebound and Subsidence
Ontario: The Geology of Isostatic Rebound - Rising Land