500 Carboniferous Lowlands
In the marine basin a laminated limestone formed, followed by deposits of evaporites (mostly gypsum) and red and green shales. Near the islands, shelly reefs developed, for example, at Gays River, Aspotogan, and East River (Mahone Bay). In the initial incursion of seawater, the intermontane basins and much of the surrounding area was flooded. The limestone deposited at that time lies on the Horton deposits and, where formerly dry land was covered, directly on the underlying topography. As the basin enlarged, later deposits of Windsor rocks were laid directly onto the older rocks of the basin margin, as can be seen in Mahone Bay, St. Margarets Bay, and on the eastern side of the Cape Breton highlands. Windsor deposits attain a thickness of 450 m in the Shubenacadie area and up to 750 m in Cape Breton.
At the end of the Windsor period, the land rose slightly and the sea withdrew to the east. Red and purple siltstones, shales, and sandstones (Canso Group) were deposited in streams and lakes. The strata may once have been very extensive across Nova Scotia but are now found in only a few major areas: around St. Georges Bay, the Strait of Canso, Stellarton-Mount Thom, and the Stewiacke Valley. They give red or purplish soils and, when exposed on the coast (e.g., Janvrin Island), bright red-coloured cliffs. This period was relatively quiet geologically; there were no tectonic upheavals, and the topography was subdued. The Early Carboniferous deposits were by this time very thick and had buried the lower elevations of the terrain. Rivers developed wide valleys with broad floodplains and estuaries. Sediments deposited in the environment had been compacted to fine sandstones, black shales, and thin coal seams (Riversdale Group). These strata also may once have been very extensive, but deep erosion has confined existing deposits to a few areas: a fringe around the Cobequid Hills, Pomquet, Port Hood, Broad Cove to Margaree Harbour, and Port Hawkesbury to St. Peters.
About this time, conditions became suitable for the proliferation of fern-like swamp plants, which flourished in extensive wetlands across the flat landscape. Great thicknesses of organic deposits accumulated and were compressed (Cumberland, Pictou, and Morien groups). These Late Carboniferous strata, which are predominantly thick sandstones and shales, cover almost the entire area north of the Cobequids and about half of Cape Breton County. The major coalfields of Springhill, New Glasgow-Stellarton, and the Sydney area are all in this group.
Carboniferous strata are relatively unmetamorphosed because, on a geological scale, they were never deeply buried. However, they were affected by compressive crustal movements during the Permian and Jurassic periods. The most intensely affected area was a band across the northern part of the province from Chignecto Bay, through the Pictou coalfield, and up through the Aspy Valley in northern Cape Breton. Resistant strata such as the Late Carboniferous sandstones and the Horton grits were thrown into open folds, whereas the softer strata in the zone, such as shales and gypsum, were distorted and crushed. There was also movement along the Cobequid-Chedabucto and Aspy faults and related movement along associated parallel and crosscutting faults.
Carboniferous deposits accumulated to a depth of many thousands of metres and engulfed most features of the old landscape. The Early Permian erosion has removed hundreds of metres of Late and Middle Carboniferous strata, exposed the underlying Windsor and Horton group blocks, and revealed ridges and valleys of the old erosion surface upon which these beds were deposited. A wide range of different rock types, with different responses to erosive forces, is now exposed. The topography reflects both this differential resistance, the structural character (folds and faults) of the area, and the relationship between the Carboniferous strata and the underlying rocks.
The upland areas are underlain by resistant Horton deposits. The rolling upland which lies between the Chedabucto and St. Marys faults has been affected by folding and faulting to quite a degree, yet it remains a rather featureless elevated area across the central mainland (District 570). This suggests that the topography reflects the more uniform resistance of the different rocks, and therefore a similar response to the forces of erosion.
The Cape Breton uplands are underlain by Horton strata, interfolded with Windsor deposits. A large area in western Cape Breton exhibits strong relief and is varied and interesting. Windsor Group limestones and gypsum have been eroded to form the deep valleys occupied by the Baddeck, Middle, and Margaree rivers. Coastal fringe deposits skirt the Cape Breton highlands and form narrow coastal plains at the base of steep cliffs (District 550). Resistant Horton sandstones form an upland plateau surface which these valleys dissect.
The intervening hilly areas of the Carboniferous Lowlands have a topographic character transitional between lowland, plain, and upland. Faults transect the basins and often set strata of different resistance against each other. Downfaulted younger strata are set against older strata and are thereby preserved, for example, the Pictou Valleys (Unit 582).
When anhydrite comes in contact with water, it expands and changes to gypsum. Gypsum is readily dissolved by rainwater and, when it lies above the permanent water table, it crumbles and washes away, leaving behind a small amount of reddish clay. Joints in the gypsum beds are enlarged and often subterranean channels are formed. Streams flow through these channels, sometimes enlarging them into caverns. If the roof of the cavern collapses, a sinkhole forms; if the roof of a channel falls in, a long gully with vertical sides is left.
Often the ground over gypsum is so closely covered by pits that only narrow crumbling ridges exist at the surface. The depressions may be underlain by holes or channels, and the whole area is treacherous to walk across.
A good example of karst topography exists at Amherst Point; another is found behind the Kings-Edgehill School in Windsor. Both locations have a number of sinkholes, with the largest ones found at Windsor. Caves are infrequent, but a well-developed one called Hayes Cave occurs near South Maitland. This cave can be penetrated for 400 m and has a maximum width of 60 m and a ceiling reaching 22 m. Sinkholes that become plugged form sinkhole ponds which have alkaline water with characteristic plants, such as Stonewort, and abundant molluscs and amphibians.
Overall there is little surface water, except where glacial deposits have impeded drainage to create the few lakes found in the Region. There are exceptions where drainage is very slow on the flat heavy clays of the Stewiacke Barrens, where extensive peat bogs have formed (District 540), and on the very flat isthmus by which Nova Scotia is joined to New Brunswick (Unit 523).
Conductivity levels, and hence productivity, tend to be highest where surface waters drain areas consisting mostly of limestone and gypsum. The levels of pH range between slightly acidic to very alkaline. Infiltration rates are relatively high in the porous soils of this Region and, consequently, groundwater recharge is high.
Winters are cold, though not severe. January mean daily temperatures are less than 6°C. Because of the influence of the Atlantic, fall temperatures in the Sydney area are somewhat higher. Spring comes later to those areas near the coast because of the ice cover and persistent cold water. Mean daily temperatures rise above freezing before the end of March, and the growing season is under way before the end of April. Spring is later at higher elevations. Temperatures warm quickly on the mainland but stay cool in Cape Breton and along the coast of the Gulf of St. Lawrence because of winds off ice-covered waters.
By July the whole Region has warmed to a mean daily temperature of over 17°C. Mean daily temperatures of less than 0°C return in November in the mainland interior, and in early December in the rest of the Region.
The total annual precipitation varies throughout the Region. In general it is drier towards New Brunswick, where parts of the Northumberland Plain (Unit 521) receive less than 1000 mm, and wetter in Cape Breton, which receives 1200 to 1600 mm. Snowfall is heavy in the interior and in the Dissected Plateau (District 590) of Cape Breton, but lighter near the coast. The snow-cover season lasts more than 130 days in all areas, except northern Cape Breton and parts of the mainland interior where it can exceed 140 days.
Early spring fogs are a feature along the Northumberland Strait because of the influence of the cold seawater on warm winds. The frost-free period lasts less than 100 days in the interior but lengthens to 140 days or more along the coast and around Sydney. The number of accumulated growing degree-days is high, particularly along the North Shore, where the warm summer waters of the Northumberland Strait boost summer temperatures.
Gypsum areas are usually overlain by glacial tills rather than by soils developed in situ, and exhibit a variety of soil types. However, because some gypsum has usually mixed into the tills, the local soil is often improved in structure and permeability. For this reason, the soils in gypsum areas are usually well-drained, even when otherwise fine-textured. The soils are also less acidic because of the influence of the gypsum. One type of soil commonly associated with gypsum is the Falmouth series, developed from a clay loam till deposited over gypsum. Falmouth soils can be important for agriculture, but when they occur over gypsum, their use is often limited by the sinkhole (karst) topography.
The main influences on the regional vegetation are the warm summers and cold winters, the heavier soils, and extensive disturbance through logging, fires, and farming. The Windsor Lowlands near Windsor and Truro grow mostly softwoods - Red Spruce, Black Spruce, Balsam Fir, Red Maple, and Eastern Hemlock. On the Northumberland Plain, where landforms are level and drainage is often poor, Black Spruce, Red Spruce, and Balsam Fir are the most common species, sometimes mixing with pine, Red Maple, or shade-tolerant hardwoods. In Cape Breton, White Spruce and Balsam Fir dominate the lowlands, while Red Maple, White Birch, and Yellow Birch are more common on the hilly lands. On the higher ground near Lake Ainslie, better drainage and cooler summers result in larger numbers of shade-tolerant hardwoods.
Bogs are generally not as prominent a feature here as in areas of more impermeable bedrock, but they are still common in the Windsor Lowlands, Bras dOr, and Sydney areas. Salt marshes and freshwater marshes are abundant. Rich intervale lands in central mainland areas and on Cape Breton Island often provide habitat for rare or unusual Alleghanian plant species.
The vegetation of gypsum areas is influenced by the calcareous nature and dryness of the soils and by a karst topography that limits disturbance through forestry and agriculture. The main form of disturbance associated with gypsum is mining, but this is now mostly confined to deep, unweathered deposits; gypsum outcrops and cliffs are more likely to be left untouched. Mixed forest (often including Eastern Hemlock, Red Spruce, and Red Oak) is interspersed with bare or scrubby areas where the soil is too thin and dry to support tree growth.
Botanical interest is provided by a number of rare or unusual plants that survive in gypsum areas because of the comparative lack of competition. The flowers are best in the early spring, before the soil becomes parched. Fleabane can be found growing on the crumbling cliff faces, and above it on the cliff tops, Gypsum Ragwort grows. Trout Lily and Yellow Ladys-slipper can be found beneath trees on the plateau. Several hardy shrubs exist here, including Round-leaved Dogwood, Buffalo Berry and Shrubby Cinquefoil. Some of these plants require basic soils, while others (cinquefoil and Yellow Ladys-slipper) can also be found in acidic bogs, where the mechanisms to reduce evaporation, which are so necessary on the dry gypsum, help to prevent the plant from being poisoned by excessive take-up of acid water. Rarities occasionally found in gypsum areas include Leatherwood and the Rams-head Ladys-slipper.
Small-mammal diversity ranges from low (coastal marshes) to high (Ainslie Uplands), depending upon habitat. In agricultural areas an open-land mammal fauna is found: fox, raccoon, and skunk. In the wilder, less-accessible parts of the Region, moose, deer, and some bear can be found. Muskrat and mink are plentiful along streams and rivers. The gypsum provides calcareous soils, which support the greatest diversity of land snails found in Nova Scotia. The caves in gypsum provide hibernating sites for bats. Productive aquatic habitats support a more diverse freshwater fauna than is found elsewhere in the province.
In the Gulf of St. Lawrence the warm summer water temperatures permit the existence of disjunct populations of Virginian marine fauna. The Bras dOr Lake has an impoverished marine fauna.
This Region provides important freshwater and coastal habitats for waterfowl.
In the past, hydro power was harnessed by grist-mill waterwheels. Now hydroelectric stations operate on various waterways which have been significantly altered to harness maximum hydro energy. Forest management has been intensive in this Region and has supplied diverse industries, including shipbuilding.
Mineral deposits have been exploited, including manganese, gypsum, anhydrite, barite, clay and shale, copper, salt, limestone, and coal. The mining of coal from the Sydney Coalfield and Pictou Valleys has been a major factor in the industrial and social development of Nova Scotia. There are several coal-fired electricity-generating stations in this Region. Sand and gravel deposits and sandstone quarries have also been important to the construction industry.
Coastline areas of the Carboniferous Lowlands have relied on the economically important fisheries of the Northumberland Strait and around Cape Breton. Many rivers of this Region are good for salmon fishing. Hunting, fishing, and other recreational activities are widespread. Scenic vistas and cultural heritage museums also attract tourism to the Carboniferous Lowlands.