Saint Lawrence Lowlands
Encyclopedia
The St. Lawrence Lowlands is an ecoregion
of Mixedwood Plains
and a physiographic region of Canada
and the United States
. It is sometimes named the "Great Lakes/St. Lawrence Lowlands", but that name improperly includes the Great Lakes Basin
which, while it might drain to the Atlantic Ocean by way of the St. Lawrence River, is part of the Canadian Shield
physiographic region.
The St Lawrence lowlands have deep, arable soils deposited during the last glaciation, when the Canadian Shield was scraped clean of all rocky soil, which was pushed south. The Great lakes-St.Lawrence Lowland is a bowl-shaped depression in the Great Lakes area (excluding Superior). It was carved out by ice sheets in the Pleistocene glaciation, about 10,000 years ago when the Lauretide ice sheet retreated. The ice sheet pushed the land down. Right now, the land is rising up (isostatic rebound). The Great Lakes basin was gouged out and then filled with water which drained to the ocean by way of the deep faultline of the St. Lawrence. The primary defining historic feature of the Lowlands is therefore the presence of deep soils within the watershed and estuary of the St. Lawrence River. This feature occurs in more than one distinct *Peninsular Ontario south and west of and the surrounding area, including the lower Ottawa Valley
and the St Lawrence below the Thousand Islands
as far as Quebec City
The Lowlands are split into these subregions by intrusions from adjacent physiographic regions. Peninsular Ontario lowlands are separated from the lowlands of the lower St Lawrence at the Thousand Islands by the geologic feature called the Frontenac Axis
, where ancient granites of the Canadian Shield cross over and become the Adirondacks. The next notable pinching occurs at Quebec City, where again the Shield meets the shore. Anticosti and Newfoundland, both being islands, are separated by stretches of open salt water.
There are some differences in terminology by Canadian and American geographers. American geographers group the lowlands of the Great Lakes basin with the Great Plains
as part of the Interior Plains
, while for Canadian geographers these are separated by hundreds of miles of harsh Shield. American geographers group the Adirondacks of New York into Appalachia and do not acknowledge their common origins with the Shield intrusion into Minnesota, again because of wide separation.
Ecoregion
An ecoregion , sometimes called a bioregion, is an ecologically and geographically defined area that is smaller than an ecozone and larger than an ecosystem. Ecoregions cover relatively large areas of land or water, and contain characteristic, geographically distinct assemblages of natural...
of Mixedwood Plains
Mixedwood Plains
The Mixedwood Plains Ecozone is the Canadian ecozone with the most southerly extent, covering all of southwestern Ontario, and parts of central and northeastern Ontario and southern Quebec along the Saint Lawrence River...
and a physiographic region of Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
and the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. It is sometimes named the "Great Lakes/St. Lawrence Lowlands", but that name improperly includes the Great Lakes Basin
Great Lakes Basin
The Great Lakes Basin consists of the Great Lakes and the surrounding lands of the states of Illinois, Indiana, Michigan, Minnesota, New York, Ohio, Pennsylvania, and Wisconsin in the United States, and the province of Ontario in Canada, whose direct surface runoff and watersheds form a large...
which, while it might drain to the Atlantic Ocean by way of the St. Lawrence River, is part of the Canadian Shield
Canadian Shield
The Canadian Shield, also called the Laurentian Plateau, or Bouclier Canadien , is a vast geological shield covered by a thin layer of soil that forms the nucleus of the North American or Laurentia craton. It is an area mostly composed of igneous rock which relates to its long volcanic history...
physiographic region.
The St Lawrence lowlands have deep, arable soils deposited during the last glaciation, when the Canadian Shield was scraped clean of all rocky soil, which was pushed south. The Great lakes-St.Lawrence Lowland is a bowl-shaped depression in the Great Lakes area (excluding Superior). It was carved out by ice sheets in the Pleistocene glaciation, about 10,000 years ago when the Lauretide ice sheet retreated. The ice sheet pushed the land down. Right now, the land is rising up (isostatic rebound). The Great Lakes basin was gouged out and then filled with water which drained to the ocean by way of the deep faultline of the St. Lawrence. The primary defining historic feature of the Lowlands is therefore the presence of deep soils within the watershed and estuary of the St. Lawrence River. This feature occurs in more than one distinct *Peninsular Ontario south and west of and the surrounding area, including the lower Ottawa Valley
Ottawa Valley
The Ottawa Valley is the valley along the boundary between Eastern Ontario and Western Quebec along the Ottawa River. The valley is the transition between the Saint Lawrence Lowlands and the Canadian Shield...
and the St Lawrence below the Thousand Islands
Thousand Islands
The Thousand Islands is the name of an archipelago of islands that straddle the Canada-U.S. border in the Saint Lawrence River as it emerges from the northeast corner of Lake Ontario. They stretch for about downstream from Kingston, Ontario. The Canadian islands are in the province of Ontario, the...
as far as Quebec City
Quebec City
Quebec , also Québec, Quebec City or Québec City is the capital of the Canadian province of Quebec and is located within the Capitale-Nationale region. It is the second most populous city in Quebec after Montreal, which is about to the southwest...
- A narrow ribbon of land along both shores of the lower St Lawrence Estuary, hemmed in on the north shore by the Canadian ShieldCanadian ShieldThe Canadian Shield, also called the Laurentian Plateau, or Bouclier Canadien , is a vast geological shield covered by a thin layer of soil that forms the nucleus of the North American or Laurentia craton. It is an area mostly composed of igneous rock which relates to its long volcanic history...
and on the south which faces into the flow of the river and has thus accreted alluvial soils from the Great Lakes basin
The Lowlands are split into these subregions by intrusions from adjacent physiographic regions. Peninsular Ontario lowlands are separated from the lowlands of the lower St Lawrence at the Thousand Islands by the geologic feature called the Frontenac Axis
Frontenac Axis
The Frontenac Axis is an exposed strip of Precambrian rock in Canada and the United States which links the Canadian Shield with the Adirondack mountain range in New York, an extension of the Laurentian mountains of Québec. The axis separates the St. Lawrence Lowlands and the Great Lakes Lowlands....
, where ancient granites of the Canadian Shield cross over and become the Adirondacks. The next notable pinching occurs at Quebec City, where again the Shield meets the shore. Anticosti and Newfoundland, both being islands, are separated by stretches of open salt water.
There are some differences in terminology by Canadian and American geographers. American geographers group the lowlands of the Great Lakes basin with the Great Plains
Great Plains
The Great Plains are a broad expanse of flat land, much of it covered in prairie, steppe and grassland, which lies west of the Mississippi River and east of the Rocky Mountains in the United States and Canada. This area covers parts of the U.S...
as part of the Interior Plains
Interior Plains
The Interior Plains is a vast physiographic region that spreads across the Laurentian craton of central North America.-Geography:The Interior Plains are an extensive physiographic division encompassing 8 distinct physiographic provinces, the Interior Low Plateaus, Great Plains, Central Lowland,...
, while for Canadian geographers these are separated by hundreds of miles of harsh Shield. American geographers group the Adirondacks of New York into Appalachia and do not acknowledge their common origins with the Shield intrusion into Minnesota, again because of wide separation.