400 Atlantic Interior
| Characteristics
| Geology | Climate | Fresh Water | Soils Plants | Animals | Cultural Environment Topics & Habitats |
Regional Characteristics
Inland from the coastal forest, the immediate climatic influence of the Atlantic Ocean is replaced by slightly warmer summers and cooler winters with much less wind exposure. The planed surface of the old, hard rocks is tilted gently to the southeast, and some of Nova Scotia's longest rivers flow across this surface. Most of
the province's lakes have been created by glacial action on the relatively flat surface. Vegetation varies from the mature spruce-hemlock-pine forests common on the Kejimkujik Drumlins (Unit 433) to the heath vegetation on the Granite Barrens (District 440) (see Figure 11).
Geology
The Atlantic Interior has three main groups of rocks: slate and
 |
| Sporting Lake Click to enlarge |
Meguma Group
The rocks of the Meguma Group are Cambrian to Silurian in age. This group has been divided into the Goldenville Formation (after a mining area in eastern Nova Scotia where the strata are well exposed) and the Halifax Formation. The Goldenville Formation is made up of greywacke (a quartz-rich rock containing some clay),
and the Halifax Formation is made up of slates.
Meguma Group strata are widely exposed across the Region and underlie about half of the terrain. They were deposited in an extensive offshore basin in which conditions stayed the same over wide areas and for long time intervals; consequently, they are rather uniform in colour and texture wherever they are found.
Gold deposits have formed within the Meguma on domes and plunging anticlines where the strata became fractured by folding. The richest veins usually occur in the zone of maximum curvature, with the largest veins in tightly folded anticlines. The veins were apparently deposited from solutions that arose deep within the lower areas and penetrated up through the fractures and along the bedding planes.
The entire thickness of the Meguma Group is unknown, because its base cannot be seen and its top has been eroded away. A section of Goldenville about 5,650 m thick has been measured between Sissiboo Falls and Weymouth in Unit 411; this appears to be close to the maximum exposed at present. Similar thicknesses are indicated in eastern Nova Scotia. About 3,650 m of the Halifax Formation have been deposited, and perhaps much more in the vicinity of Halifax. This thins out to a maximum of 1,225 m or less in southwestern Nova Scotia.
White Rock Formation
In the Silurian, following the deposition of the Meguma Group, one or more volcanic centres developed, probably close to what is now the coastal area near Yarmouth. A series of strata composed of (about 50 per cent) lavas and ash and (about 50 per cent) sandstone and mudstone built up. These strata are jointly called the
White Rock Formation today. They are preserved in a series of synclines in the Yarmouth area, at Cape St. Mary, along the Sissiboo River, at Bear River, and in the Gaspereau area. The White Rock Formation is thickest at Yarmouth, where 3,000 m have been measured with only the bottom exposed, and it becomes progressively thinner
to the north.
During the Late Silurian to Early Devonian period, the Meguma and White Rock strata were folded and changed by heat and pressure during the crustal disturbance called the Acadian Orogeny. The strata folded much as a rug would if its edges were pushed together. For the most part, the axes of the folds lie parallel to the long axis of the province and form an arc from Yarmouth to Canso. They lie an average of 5 km apart and can be traced lengthwise for up to 150 km. The folds are sometimes symmetrical, but they are often asymmetrical and often so tight that the crests have turned sideways and become overturned.
While lateral pressure was exerted, the temperature rose to a maximum of 650°C and the character of the original strata was changed. Under these conditions, the chemical elements of the rocks recombined to form a characteristic series of minerals: garnet, staurolite, andalusite, and sillimanite. The temperature and pressure conditions of this regional metamorphism can be estimated by examining the minerals that formed, because each only forms when certain temperatures and pressures exist.
Surveys carried out in the 1950s and 1960s reported soils developed from mica and hornblende schists, particularly in Yarmouth and Digby counties. Correlation of these soils with the geology is unclear, because zones of intense metamorphism of the quartzites are as frequent in Unit 412 as in Unit 411.
Granite
The third main group of rocks in the Atlantic Interior falls under the name "granite." This familiar, coarse-textured rock actually includes a whole range of related but different rock types. They have a variety of colours, textures, and compositions but commonly contain large greyish or pink crystals of potash feldspar in a matrix
of smaller crystals dominated by quartz and mica.
Most of the granite lies in a huge body called the South Mountain Batholith, which is exposed in a giant arc from Yarmouth County northwards to the edge of the Annapolis Valley and around to Halifax. This batholith intruded during the late stages of the Acadian Orogeny as a hot, thick liquid. This magma rose by penetrating the overlying Meguma strata, broke off blocks, and assimilated them. In places near the contact, blocks of Meguma country rock can be seen in various stages of assimilation, as xenoliths. In some places they look almost unchanged, whereas in others they have been almost entirely absorbed and can be seen only as ghosts.
The heat given off during the intrusion, and later as the magma cooled, baked the surrounding Meguma strata and created a narrow contact aureole. In this aureole characteristic minerals have developed, in particular cordierite which is round and black and gives the slates a spotted appearance. Good examples of the changes that took place close to the contact can be seen west and north of the Northwest Arm near Halifax.
Pre-Carboniferous Erosion
Following the Acadian Orogeny and the emplacement of the granite came a period of very rapid erosion. Material several miles thick was removed within about 10 million years and the granite was exposed. The sediments generated during this erosion were carried off and deposited elsewhere. The erosion surface was later to
form the basement upon which Carboniferous strata were deposited.
Development of the Present Topography
Probably during the Cretaceous the whole area was eroded down to a fairly level surface, which is now more or less coincident with the overall level of the Atlantic Interior. Large areas of granite became exposed, some of which now form domes or high, rounded hills. The overlying, folded greywacke and slates were eroded
away and are now found mainly around the edges of the granite, or in what were the lower areas between the granite cupolas and domes. The slates, being the uppermost strata, were worn away when the Meguma folds were planed off, and the greywacke was exposed underneath. The slates are still preserved in many places in the
synclinal troughs and now occur as long, narrow bands running east and west. The folds are steeper and more compressed east of Halifax than to the west, so that the slates between Halifax and central Guysborough County are in rather narrow bands, while northward in Hants County they form wide zones. The general pattern can be
seen on the geological maps. Only in western Lunenburg County, and in adjacent Queens and Annapolis counties, are large areas of slate found.
Faults
The topography of southwestern Nova Scotia has not been influenced significantly by faults. However, east of Halifax, where there are many faults and the strata are also more intensely folded, the opposite is true. From St. Margarets Bay to Guysborough, the Meguma strata are shattered by innumerable faults, a number of
which affect the outline of the coast and the topography inland. One at Cole Harbour continues inland up the valley of Lake Major; another at Sheet Harbour controls the upper bend of the harbour, continues up the deep valley of the West River, and stretches inland practically across the entire Southern Upland. The long, straight
harbours at Indian Harbour, Country Harbour, and New Harbour in eastern Guysborough County are also determined by faults. The fault at Country Harbour is the most prominent: there, a deep, straight-sided channel penetrates inland about 25 km to form one of the best natural harbours in the world.
Topography
When viewed from North Mountain across the Annapolis Valley, or from an elevation looking south towards the escarpment of Guysborough County, the surface of the Atlantic Interior presents an almost even, level skyline. This uniform surface is also evident inland, as in northern Annapolis County. There the upland surface
is around 150 m above sea level and has a relief of barely 15 m. East of Halifax, near the coast, the river valleys are deep and cut far below the surface, but even here the uniform height of the upland surface is evident from a distance. In the southwest there is very little relief, and the land is either almost flat over large areas or has
only low ridges and wide, shallow valleys.
The upland surface slopes southeast or directly towards the Atlantic coast, but there is also a distinct lowering of the elevation, and more uniform topography, southwestwards towards the Gulf of Maine. This is particularly evident from Queens County to Yarmouth.
The highest points along the northern border are rounded hills that rise gently from the surrounding country. Two granite knolls south of Kentville are typical: one of them, north of Lake George, rises to more than 275 m, and another, southwest of Gaspereau, is around 260 m. Several slate hills in the same general area are only slightly lower, at nearly 245 m. In northern Annapolis County, the highest area, southwest of Bridgetown, is a little over 275 m high, and from there the surface slopes gently down to Brier Island. In eastern Guysborough, along the northern edge of the narrow band of upland, the elevation is about 225 m above sea level. Only occasionally throughout the Atlantic Interior does a hill rise significantly above the surrounding area. One of these is Aspotogan Mountain on the peninsula east of Chester, which reaches a height of 145 m in an area with an average elevation of barely 75 m.
Granite Area
Granite comprises the most extensive areas of the Atlantic Interior and reaches the highest elevations. The rock is massive and seems resistant to chemical change, although post-glacial weathering has affected all exposed surfaces. Low, rounded hills or shapeless ridges generally rise less than 20 m above the mean elevation,
with intervening broad, shallow depressions which are too irregular to be called valleys. High knolls occur occasionally, but the slopes are rounded and subdued throughout with no particular pattern or design. The drainage is poor, and sluggish rivers or streams meander from one shallow lake to another. Large boulders line these
channels, and dot the lakes.
Greywacke Area
The greywacke topography is somewhat more varied. In eastern Nova Scotia, on the northern border of Halifax and Guysborough counties, the surface is much like a plateau, with long, low ridges running east and west. Large, angular blocks of greywacke cover the ground and the soil is usually thin and acid. The intervening
hollows are swampy and have their long axes generally oriented parallel to the strike of the strata; drainage is impeded by deposits of glacial drift. The river channels in the interior are shallow because the streams run down the tilted erosion plain across the fold axes and cut across layers of resistant strata. Near the Atlantic coast,
the topography is frequently more uneven and the stream channels are deeper, but even here the land tends to be monotonous and covered with scattered rocks of all sizes. Greywacke is also common in southwestern Nova Scotia, where, again, the topography tends to be flat and monotonous.
Slate Areas and Drumlins
The slate areas present a more interesting and varied topography than the areas of greywacke and granite. Slates weather relatively easily. The surface of the slate areas has been planed off, and the resultant loose material has been carried away to form a deep glacial drift with a high percentage of silt and clay. The advancing
glacier moved over the area like a bulldozer, scraped off the weathered material, carried it for a kilometre or so, and then, overloaded by the mass of material, dropped it and sometimes shaped it into drumlins.
Where material is sufficient, drumlins produce a rolling topography. The drumlins may be isolated, may overlap to form irregular hills, or may be joined to make beaded ridges. The slate areas of Lunenburg County represent typical drumlin country, a very distinctive type of topography which can be recognized as soon as one enters it. Small, oval hills are scattered over the landscape, with ponds or lakes in the hollows between them. On land they appear as swarms, which are often quite well defined geographically.
Climate
The Atlantic Interior is a large, contiguous region that includes considerable climatic variation but has basically an inland, lowland climate sheltered from direct marine influences. The climate is characterized by cold winters and warm summers. Variations in temperature and precipitation are, to a certain extent, governed by
distance from the Atlantic coast and by latitude.
The mean annual temperature varies from 1°C towards the southwestern tip of the province to 5°C and higher in the more inland areas. In most of the Region, January mean temperatures are below -5°C and are generally warmer towards the coast. Mean temperatures rise above freezing by the end of March, with spring arriving somewhat earlier in the southwest. By July, most of the Region has warmed to a mean temperature in excess of 17.5°C, except in the more northerly areas of the Region in Halifax and Guysborough counties. The area around the LaHave drainage basin and Kejimkujik Lake tends to warm up earlier and has hotter summer temperatures. Freezing temperatures return to the Region by the second week in December, and a little later near the southwestern tip.
The mean total annual precipitation ranges from 1200 to 1600 mm. The drier areas are found near the southwestern tip and towards the interior. Mean total snowfall ranges from 150 cm near the coast to 250 cm or more in higher areas and further inland. The snow-cover season varies from about 110 days in the southwest to more than 130 days further north.
The frost-free period varies from less than 100 days in the interior to more than 140 days in the southwest. The number of accumulated growing degree-days are highest in the southern part of the Region and taper off towards the north.
Fresh Water
Drainage patterns in Region 400 are typically deranged, and surface water is retained in a disorganized series of streams, lakes, and bogs. Chains of lakes, streams, and stillwaters occur in the interior, with low ridges following the trend of the underlying strata. Many of the streams are slow-flowing and interrupted by shallow,
rocky ponds and lakes. In Queens and Shelburne counties the rivers and streams tend to cut across bands of harder rock to form rapids and low waterfalls, as along the Medway and Mersey rivers. In Yarmouth County the folds of the strata bend southward, and consequently the flow of the streams is along the strike of the structures
rather than across them. The streams flow slowly through wide, shallow valleys, where lakes and stillwaters also occur. In parts of Shelburne County the land is practically flat as far as the eye can see, as if it had been planed off to a level surface to form broad expanses of poorly drained areas and bogs. Ponds and lakes are common in
the hollows between drumlins. The highest elevation is near the northern border of the Region, where the divide between streams draining north and those flowing south makes a great arc, north from near Pubnico almost to the slope of the Annapolis Valley and around to the Waverley lakes near Halifax.
Surface waters are dystrophic throughout this Region. Primary productivity tends to be low and most lakes are oligotrophic. Surface water also tends to be low in dissolved solids, providing little buffering capacity. Combined with the low buffering capacities of the thin soils and tills associated with the quartzite, slate, and granite bedrock, much of the fresh water in this Region is susceptible to acidification. Surface water is less acidic in the drumlin areas.
Groundwater in this Region is stored and transmitted through fractures and joints and along fault and contact zones in the bedrock. It tends to be low in dissolved minerals but, like the surface water, is susceptible to acidification from acidic runoff and to discolouration from contact with naturally occurring minerals such as iron and manganese associated with granite and quartzite. The slates of the Halifax Formation tend to have a good overburden of till that somewhat buffers the natural sulphides that can contaminate ground and surface waters.
Soils
The major factors affecting soil development in this Region are the resistant granite and quartzite bedrock, the undulating and often poorly drained terrain, and the influence of finer-textured tills transported by glacial action from Carboniferous areas. Over most of the Region, strong scouring has left a thin, bouldery till cover
on which humo-ferric podzols predominate, with considerable areas of gleysol, Rockland, and peat. Coarse, bouldery, sandy loams have formed in granitic areas, while on quartzite the stony, sandy loams have slightly finer textures. Where soils developed from till over slates and schists, vigorous vegetative growth is prevalent, in
marked contrast to that of the quartzite soils. The soils themselves are usually very permeable, but drainage is often impeded by topography or underlying bedrock. Soils are strongly leached and very acidic. An important feature of the soils of this Region are the drumlin fields. Soils formed on drumlins are often better drained, finer
textured, deeper, and somewhat more fertile.
Plants
The Atlantic Interior covers three of Loucks' Forest Zones. The largest area falls within the predominantly softwood Red Spruce, Hemlock, Pine Zone. The LaHave basin, between Kejimkujik Lake and the LaHave River, is in the Sugar MapleHemlock, Pine Zone. The hilly areas around the Musquodoboit River fall within the
Sugar Maple, Yellow BirchFir Zone.
The main influences on regional vegetation are the inland climate with its warm summers; the sandy, acid soils; the mixed drainage; and extensive disturbance by fire and logging. Softwoods dominate, but shade-intolerant hardwoods frequently occur on burnt-over land, and pockets of shade-tolerant hardwoods are found on higher, better-drained sites. Red Spruce and Eastern Hemlock were once abundant throughout much of the Region, but both have been depleted by cutting.
In the southern part of the Region, south and west of a line from Windsor to Halifax, where the soils are generally better drained and summer temperatures are slightly higher, spruce and Eastern Hemlock are found in association with Red Oak and White Pine. Balsam Fir and Red Maple are found on disturbed sites, but the fir usually disappears within 30 years. Beech was once abundant but is now found mostly on drier ridges. Ash is found on seepage slopes throughout the Region, particularly on the sides of drumlins. Bogs and swamps are very common, particularly towards the southwestern tip of the Region.
In the more northerly part, north and east of a line from Windsor to Halifax, where summer temperatures are slightly cooler and drainage is poorer, Red Spruce and Eastern Hemlock are found with Black Spruce and Balsam Fir. Sugar Maple and White Pine are found on rolling hills, particularly inland. Black Spruce swamps and peat bogs are extensive, and Red Maple, aspen, and Wire Birch predominate as post-fire species, rather than Red Oak. On the rolling hills around the Musquodoboit Valley, higher elevations and better drainage favour shade-tolerant hardwoods and mixedwoods.
The southern part of this Region is distinguished by the presence of Southwest Flora, or Coastal Plain Flora. This is a group of plants normally restricted to more southern ranges, but because of the milder climate in Nova Scotia, they are able to establish themselves here.
Animals
Softwood and mixedwood forest habitats predominate in this Region, favouring fauna of a more boreal association. Disturbance is widespread, and there are very few areas of mature forest. Moose and bear are scattered with a concentration in the area of the brush barrens east of Yarmouth. With the exception of these
barrens, deer are found throughout the Region. New growth on recently cut-over or burnt areas provides good forage for ungulates. Bogs and inland barrens are common. Small-mammal diversity is low to moderately high, depending upon habitat. Two species, White-footed Mouse and Southern Flying Squirrel, are disjunct in Nova
Scotia from other North American populations. The Southern Flying Squirrel has a restricted distribution (Kejimkujik Park), but the White-footed Mouse distribution coincides with the boundaries of the Region. Lakes and streams cover a considerable proportion of the Region, but the very acidic and deeply coloured character of the
water supports an impoverished freshwater vertebrate fauna.
Cultural Environment
The forests of the Atlantic Interior have been commercially managed since the eighteenth century and have experienced repeated fires. Log drives took the timber from the interior to sawmills on the coast where it was exported as lumber. Many sawmills still operate in this Region.
The vigorous regeneration of Balsam Fir has led to the establishment of the Christmas tree industry, centred in District 430. Small pockets of agricultural land are scattered through the Region, often in association with drumlins (District 430). The Lunenburg Drumlins attracted German settlers, and Loyalist, Irish, and Scottish immigrants farmed the Annapolis, Ponhook, Kejimkujik, and Eastern Shore drumlins. Many marginal farmlands were later abandoned, giving way to oldfield succession.
Metals and minerals mined have included gold, tin, and limestone, as well as sand, gravel, and crushed rock. Peat resources underlie much of this land. At various localities, hydroelectric power has been harnessed.
The southwestern part of Nova Scotia is the most significant archaeological area in the province. Many parts of the Atlantic Interior were important to the Mi'kmaq for hunting and fishing. Shell middens found along St. Margarets Bay (sub-District 460b) and arrowheads found along canoe routes at Kejimkujik Park (Unit 433) give evidence of former aboriginal occupation. When sport hunting developed in the latter half of the nineteenth century, Mi'kmaq guides were employed by American hunters for moose-hunting and fishing expeditions. Thus began the hunting and fishing lodge tradition in the southwestern Atlantic Interior where the Tobeatic Game Sanctuary is found. Hunting and fishing continues in many of these areas today. Other recreational land uses include canoeing, hiking, bird-watching, and camping, particularly at Kejimkujik National Park, which was established in the 1960s.
|
|