Escarpment Geology: Another part of our Living Landscape By Beth Gilhespy : o t o h P e k u D n a i r B : o t o h P It’s a crisp fall day on the Bruce Trail and I’m deep in a valley, about to start my ascent of the Niagara Escarpment. As the path steepens and I begin to lean into the hillside, I notice patches of bright red mud beneath the brown forest soil of the path. Continuing up the slope, the path steepens even more and thin layers of rock slide from under my feet. I thankfully reach a more gentle slope and continue my climb, eventually reaching the base of the prominent grey-white rock face. The Trail takes me up through a crevice and, having passed over boulders and rock fall, I finally reach my destination - the very top of the Niagara Escarpment. My ascent of the Escarpment hasn’t just It’s hard to grasp the time gap between logical time that limits us from seeing it as been a workout – it’s been a journey the formation of the Escarpment’s sedi - part of a living landscape – not just the through 30 million years of the earth’s mentary rock layers and the feature we plants and animals, but the long, slow but history. I started at the late Ordovician know and love today. When the rocks inexorable changes to the Escarpment’s Period 450 million years ago (that’s the were being formed, the earth’s continents hills, valleys and shorelines. bright red Queenston Shale that mud - as we know them were scattered about ––– dies my boots and makes the path the globe, a mountain range higher than During the late Ordovician Period, treacherous in rain) moving on to the the Himalayas dominated our own conti - approximately 450 million years ago, a early Silurian Period with its mixed beds nent which in turn straddled the equator, large, shallow sea filled an area now of sandstone, dolostone and shale, and and our very planet was spinning faster, inhabited by the Great Lakes, called the arrived at the climactic heights of the giving us 21-hour days. We may think of Michigan Basin. The climate was tropi - Amabel Dolostone, formed during the geology as the element of our landscape cal, and although the shallow sea was middle Silurian Period 420 million that remains constant, but it’s our inabili - teaming with life, plants and animals years ago. ty to comprehend the magnitude of geo - had not yet been established on land. 22 BrucE trAiL MAGAzinE SPrinG 201 5 y p s e h l i G h t All map references are 28th Edition Bruce Trail Reference. e B : o t o h P Southeast of the Michigan Basin logical features that make up the (roughly where the Appalachians are Niagara Escarpment. There’s so now) a mountain range was rising from much more to tell! Consider the collision of the North American and joining a geology hike (see page European/African plates. The rocks of 30 of this magazine) or coming these mountains were rich in iron, and out to the Fossil Glen event on rivers flowing down the mountains May 3 (see the back cover) to picked up the red, iron-rich sediment learn more about the geology of and transported it to the basin to form a our beautiful Niagara mighty delta of red mud and sand. Escarpment. In time, the sea occupying the Michigan Basin deepened and cleared, a journey Through the Queenston Shale at Gravelly Point, Peninsula, coral reefs formed, and other sediments rock layers were deposited on top of the red delta. We’ll start at the base of the Niagara Queenston shale Compaction of successive layers of sedi - Escarpment with the Queenston Shale, The Queenston Shale is one of the more ments formed the shale, sandstone and and work our way up through the layers familiar layers of the Niagara dolostone that make up the Niagara to the caprock of the Escarpment, the Escarpment. It can be found at the Escarpment. Lockport-Amabel Dolostone. Rather than Niagara River near the start of the Bruce cover each and every layer we’ll focus on Trail, and continues as far north as Cabot the more visible rock layers encountered Head, where it appears just off shore and dolostone is limestone that has been along the Bruce Trail. washes up as red mud during storms. The Queenston Shale is the remnant of altered by the addition of magnesium a large, muddy delta that was building that was present in the seawater. navigating the rock layers into the shallow continental sea to the It’s easy to become muddled when northwest of the precursor to the trying to sort out the different rock Appalachian mountains about 450 mil - lion years ago. Its red colour is due to the For the last 250 million years since the layers of the Niagara Escarpment. presence of iron (hematite) in the mud. seas of the Michigan Basin dried up, soft Here’s a hint to keep it in context. While the Cheltenham Badlands is layers of shale have continually been perhaps the best known exposure of eroding away, undercutting the harder one Queenston Shale, its existence is certain - sandstone and dolostone rock layers on el Dolost ort-Amab ly evident elsewhere on the Escarpment. top and causing them to break off, creat - Lockp ds In Hamilton, Milton and in the ing the steep face of the Escarpment. Mixed Be Brampton area, Queenston Shale was Although most evident at waterfalls on Shale Queenst (and continues to be, in some places) where erosion is accelerated, this process quarried for brick-making. Along most of of undercutting is responsible for the the Escarpment the Queenston Shale is gradual erosion of the entire Escarpment Lockport-Amabel Dolostone caprock at the top. covered by vegetation (grasses in some over the past 250 million years. Thinner layers of sandstone, shale, limestone areas, thick forests in others) that masks More recently – a blink of the eye in and dolostone in the middle. but at the same time protects and stabi - geological time – glaciers that left this Queenston Shale at the bottom. lizes the shale. Farther north near Mono region 12,000 years ago have modified Cliffs, in the Hockley Valley, and along the Escarpment’s features. Glacial melt - Think of the Escarpment as three the waterline at Colpoy’s Bay, erosion of water laden with hard boulders and cob - main layers. The bottom layer is the steep banks of Queenston Shale means bles from the Canadian Shield – called Queenston Shale, while the top is the that vegetation can’t take hold, and the erratics – scoured broad valleys and its Lockport-Amabel Dolostone, and characteristic rich red clay and grey- swirling action created potholes. Those these two layers are fairly constant green stripes are exposed. same boulders and cobbles were left throughout the length of the behind as moraines, drumlins and Escarpment. It’s the middle layers Where to see it: eskers, and cover the Escarpment that can vary widely, and the layer • Along the banks of lower Grindstone bedrock in much of the Caledon Hills you encounter will depend on where Creek, especially where the Trail cross - and Dufferin Hi-Land sections of the you are along the Bruce Trail. From es the river on a splendid bridge built Bruce Trail. Crevices formed along the Niagara to Hamilton, closest to the by volunteers (Iroquoia km 69.2) Escarpment’s edge due to the effects of Appalachian Mountains (the source • On portions of the main Bruce Trail at frost wedging. Higher lake levels carved of the sediments), there are many the Cheltenham Badlands (Caledon shoreline caves and flowerpots. middle layers – shale, dolostone, Hills Section between km 0.0 and 1.3 The geology of the Escarpment is sandstone and even some limestone. with views from the Olde Baseline Side expansive, and there’s a lot to learn From Hamilton north there are fewer Trail) about the ground beneath our feet. This of the middle layers, reflecting a • Just west of Gravelly Point at the field guide provides just a snapshot of more stable marine environment. shoreline (Peninsula Section – Gravelly some of the major rock layers and geo - Point Side Trail) www.BrucEtrAiL.orG BrucE trAiL MAGAzinE 23 i Whirlpool sandstone l A i t n I From Niagara to the Pretty River Valley : o t o area of the Blue Mountains, the h P Queenston Shale is directly overlain by the Whirlpool Sandstone. The thickest layers of Whirlpool Sandstone are to the southeast, and gradually thin in a wedge shape towards the northwest. This reflects the source of the sand, which came off the rising pre-Appalachian Mountains. t t a W n o s i l A : o t o h P cut blocks of whirlpool Sandstone in the Hoffman Lime Kiln stack, Forks of the credit, caledon Hills Manitoulin dolostone forming in a shallow tropical sea roughly The Manitoulin Dolostone can be found 444 million years ago. The formation is on the Escarpment from Hamilton north thinly bedded, and contains small fossils to Manitoulin Island. From Hamilton to and iron inclusions. the Blue Mountains it immediately overlies the Whirlpool Sandstone as that Where to see it: formation gradually thins in a wedge • Along the shoreline at Rush Cove whirlpool Sandstone overhang at shape to the northwest. From the Blue (Peninsula km 55.8 to 56.4) Grindstone creek, iroquoia Mountains north the Manitoulin • Rocky outcrops all along the high Dolostone directly overlies the ridge at Loree Forest (Georgian Peaks ) The contact between the Queenston Queenston Shale, and forms the lower- • Flat layer sitting atop the Whirlpool Shale and the Whirlpool Sandstone rep - most Silurian Bed.