Water and Land

In a world perspective, what is distinctive about Ontario’s physical geography? Certainly the province’s relatively low elevation near the centre of a continent is not unusual. What is distinctive is the presence and importance of water. Ontario lies between two great water systems: on the north the Hudson Sea, that incredible penetration of the Atlantic Ocean into interior North America, and on the south the Great Lakes, the most magnificent chain of lakes in the world. Associated with these huge bodies of water are large rivers such as the Albany and Severn in the north, and the St. Lawrence and Ottawa in the south. Over 200,000 lakes are scattered throughout Ontario, and in the north, an immense water-logged plain slopes down to James Bay and Hudson Bay. Ontario is huge. It extends more than 1,700 km from south to north 41° 41'N to 56° 50'N, that is, from the latitude of Rome almost to that of Edinburgh), more than 1,600 km from east to west (74° 25'W to 95° 9'W), and is 1,068,582 km2 in area, 10.8% of the total extent of Canada. The great size is not immediately apparent on a map because Ontario is not compactly laid out in one neat block. It has a complex configuration mainly because of the large bodies of water on its southern and northern boundaries: in the south are great jutting peninsulas set amidst Lakes Huron, Erie and Ontario, and in the north, in what is by far the largest part of Ontario, are the immense sweeping curves of Lake Superior and the sea coasts of Hudson Bay and James Bay.

Compared to many other parts of Canada, Ontario is relatively low in elevation. It ranges in relief from sea level on Hudson Bay and 75 m on Lake Ontario to 693 m above sea level at its highest point, Ishpatina Ridge, west of Lake Timiskaming. The surface, on the whole, rises gradually to broad plateaus in northern Ontario about 450 m to 600 m in elevation, and high plains in southern Ontario about 200 m to 500 m high. There is considerable local relief. In the north, deep valleys were eroded in the plateau surface to form spectacular chasms such as Agawa Canyon near Sault Ste. Marie and Ouimet Canyon near Thunder Bay. Along the north shore of Lake Superior is the most splendid scenery in Ontario, especially in the stretch from Nipigon to the U.S. border. South of Thunder Bay, for example, are the Nor’Westers, flat-topped mountains protected from erosion by resistant cap rocks. Southern Ontario has its own scenic highlights in the sharp linear ridge of the Niagara Escarpment, in gorges cut into the scarp, and in Niagara Falls.

When we look at the face of the land, it is the vegetation that gives us our main impressions of the landscape. Some 400 years ago Ontario was under a vast, almost continuous, canopy of dense forests: in the south, deciduous; in the north, coniferous; and in between, mixed. Early European visitors were vividly impressed by the few small, brightly sunlit grass and scrub openings found in sandy areas in the deciduous and mixed forest areas of the south. Other forest openings were produced in present Simcoe county by Hurons clearing small patches for agricultural use. Farther north, boreal forests dominated, and the almost continous tree cover went on and on, seemingly forever. In the Shield, cliff faces were largely bare though trees did manage to anchor themselves in the merest crevices.It was wetlands, the swamps and muskegs that produced the largest gaps in the tree cover in the north and finally completely dominated the landscape toward Hudson Bay. The cool immediate shores of the Bay were tundra, the very low vegetation of the Arctic.

The broad transition from mainly deciduous, to mixed, and finally to boreal trees is a reflection of the climatic differences found in a huge province. Precipitation is adequate for plant growth in all parts of Ontario, but not until agricultural settlers over the course of several generations had moved into various parts of the province were the full extremes of climate associated with different latitudes fully appreciated: the niceties of the varying lengths of the frost-free and growing seasons, and the temperature differences introduced by lake shores and higher elevations. In the south, of course, trees have been mostly cleared to make way for farms and cities, but in the north forests remain dominant.

In native times there were fewer than 100,000 people in what is present-day Ontario. Today the population approaches 10 million, but it is unevenly distributed. In part this is due to vital differences in resources, industrialization, urbanization and so on, but always in the background is the nature of the land, and humans must take that background into account in the ways they make their living and in their everyday lives.

An examination of the Ontario ecumene, that is, places where humans have settled as indicated by the patterns of population in 1986, reveals the great concentration of people in southern Ontario, the breaking into belts and scattered pockets to the north, and then the very sparse settlement north of the railways and major highways. We will not discuss these patterns in any detail in this chapter, but if we bear them in mind this will sharpen our appreciation of possible relationships between humans and the environment.

Rocks

Geological processes, some working over billions of years, others most strongly over the last 25,000, have shaped the outstanding features of the face of present-day Ontario.

The oldest rocks in Ontario were formed about 3 billion years ago. They are almost as old as the 4.6 billion-year-old earth. Molten material from the earth’s interior flowed through great crustal cracks into primeval seas, and on cooling solidified into igneous rocks. Gradually these rocks accumulated until they were above sea level. Once exposed to the atmosphere, the surface rock immediately was subjected to weathering and erosion by water and wind. The debris was carried into the sea and, after compaction, formed sedimentary beds. Later, at various times, folding, faulting and thrusting of rock caused the formation of great mountain ranges. Heat and pressure created new kinds of rocks out of existing igneous and sedimentary formations—metamorphic rocks such as gneisses and schists. The mountain ranges were eroded in turn. As long as mountain-building processes outpaced those of erosion, mountains grew in height, but during incredibly long, stable periods they lost out and were worn down. In the roots of former mountain ranges, now partially exposed after erosion, mineralized zones often occur making accessible minerals which are of great use to humans.

In the distant past, it is evident, Ontario was not the placid land, geographically speaking, it is today. In Muskoka there have been mountains the height of the Alps, and in the area northwest of Lake Superior there were great igneous intrusions into sedimentary beds through fissures in the earth’s crust. Always atmospheric and gravitational forces work to bring mighty mountains down to sea level, but the earth’s internal engine counters this by building up the land. These processes are invisible to humans because they take place over millions of years. But the accumulated results are impressive and formed the earth we live on.

Geologists have studied the ancient rocks of Ontario for over a century, have worked out the geological story, and have mapped the present pattern of rocks. Time periods when great geological revolutions took place, such as pronounced mountain building, have been identified and named. We need not concern ourselves with detailed subdivisions but should know that the long extent of time from the origin of the earth up to 570 million years ago is called Precambrian time. Life began in the Precambrian, but heat and pressure, creating metamorphic rocks, have altered these ancient formations so much that the visual fossil evidence of early forms of life is usually never very clear to laypersons. Toward the end of the Precambrian, mountain building ceased in present-day Ontario; the formerly restless land became a stable part of the earth’s crust and was reduced by erosion into a rugged plain not far above sea level.

After the Precambrian, this land was occasionally warped downward below sea level and then much later also upward very gradually over long periods of time. Thick deposits of limestones, sandstones and shales, formed from materials derived from highlands to the southwest of present Ontario, were laid down in seas that penetrated far into the depressed interior of the continent and covered the province of today. This was the time of burgeoning life, and many marine organisms added their skeletons to the sedimentary beds that were being formed, especially the limestones. Indeed, the names of these geological periods, Paleozoic, Mesozoic and Cenozoic mean, respectively, the times of early, middle and late life. It may be that extensive sedimentary beds covered all Precambrian rocks, but if so they were removed by erosion from much of central Ontario once the land moved gently above sea level again, exposing the Precambrian formations. Deep sedimentary strata still remain, however, and in Ontario form the surface rocks to the south and north of the Precambrian basement igneous and metamorphic rocks, and they are very important in the human development of the province. The extensive sedimentary strata in southern Ontario are called the Great Lakes-St. Lawrence lowlands, and those in northern Ontario, the Hudson Bay lowland (figure 2). The exposed part of the Precambrian rocks is well known to all of us as the Canadian Shield.

The two lowlands of sedimentary rock form gently tilted platforms with fairly even surfaces on either side of the Shield. When eroded, tilted beds of varying resistance to erosion can result in impressive long, linear ridges. Millions of years of erosion have created the high cliffs of the Niagara Escarpment which is strung across southern Ontario. The upper, more resistant sedimentary beds protect the brow of the escarpment from rapid erosion as the softer, lower beds are worn away: the great wall of the scarp remains. The erosion along the front of the scarp is uneven. Attractive valleys, such as the Beaver Valley, have been cut into the escarpment; for over 10,000 years the Niagara River has been eroding a gorge back from the face of the scarp, that is, from present-day Queenston with Niagara Falls at the cutting edge.

Ice

If the grand structure of our land was formed by what happened millions of years ago, we have to look to events of the recent past to explain the details and nuances of the present surface, especially for the origin of the parent materials on which soils are formed and plants grow. In the last million years immense continental ice sheets covered Ontario a number of times, advancing and then retreating, and then repeating this all over again. The most recent glaciation put a strong stamp on the face of the land, and that is the one which concerns us. As the ice enveloped northern North America it destroyed all vegetation, and wildlife could only retreat before inexorably advancing ice sheets. Ice, 2 to 3 km thick, covered all of Ontario 24,000 years ago. As the climate moderated, the ice melted down and retreated. By 12,000 years ago the Toronto area was uncovered, and by 8,000 years ago the ice was gone from the Hudson Bay lowland. Plants, wildlife and humans were able to occupy the land and make of it what they could.

The ice reshaped the land in two ways: erosion and deposition. When the irresistible ice lobes advanced they abraded, scratched and scraped out shallow basins in bedrock, rounded and smoothed resistant low peaks into rock knobs, dislodged and plucked pieces of weaker rock, ground up these materials and carried much rock and debris away within the ice. Later, beneath the ice sheets and at the margins, the material was deposited in all sorts of ways. Glacial drift is the inclusive term used for all forms of glacial deposits. Such deposits can take the form of extensive, rolling plains comprised of unsorted clay and rock, called till, that are plastered down beneath the ice, or of hummocky till ridges, called end moraines, that have accumulated at the margins of glaciers. Huge boulders, called glacial erratics, were sometimes carried a relatively short distance by the ice and dropped. Rapidly running meltwater sorted materials into sands and gravels and laid them down in wide aprons at the front or sides of the retreating ice lobes. Finer materials such as clay were deposited in the bottoms of glacial lakes that formed at the margins of the ice sheets when meltwater could not flow away quickly and was dammed up. These lakes lasted until new, lower outlets were opened allowing the water to drain away. Nowadays those former lake beds are flat, clay plains. The retreat of the ice was a messy business. At the end of the glaciation, however, there was a wide range of landforms and surface materials left as a legacy of the ice sheets. This resulted in a surprising variety of landscapes in Ontario even though the general elevation may be monotonously low.

Glaciation produced very different kinds of landforms in the Canadian Shield and in both lowlands. In the Shield, resistant higher rocks have been smoothed into streamlined rock knobs. Pre-existing drainage was completely disrupted. Thousands of lakes, connected by rushing rapids-filled streams, now occupy partially blocked depressions and basins. In many places sands and gravels mask bedrock, and former lake beds now form level, clay pockets and clay belts, but these are relatively small and the dominant Shield surface is hilly, rocky, rugged, terrain with much bedrock exposed and many lakes and rivers in the depressions.

By contrast the surface of the Great Lakes-St. Lawrence lowlands has an even, smoothly rolling, voluptuous appearance. On the sedimentary beds of the lowlands, deep deposits of undulating, glacial till were laid down by the ice over large areas. In places, as at Peterborough or Guelph, the till is mounded into long, gently streamlined hills called drumlins, hundreds closely grouped together consistent in alignment with the direction the ice moved. Long, narrow belts of end moraine provide locally rougher terrain in locations where the front of the ice remained for a considerable time during the glacial retreat. In a few places the limestone bedrock of the lowlands is only thinly covered by the glacial drift: at Napanee and in some areas just behind the Niagara Escarpment flat-lying, living rock is exposed.