The Pictou-Antigonish Highlands are underlain by a block of old crustal rocks which are bounded and transected by numerous faults. The Unit stands at an average elevation of 245 m but is dissected into steep-sided hills and valleys where faults cut across the resistant massif. The two most important faults are the Hollow Fault in the northwest and the Cobequid-Chedabucto Fault on the south. These two faults accommodated extensive lateral slip motion as the crustal sections were slipping into place during the formation of Nova Scotia.
The strata within the Pictou-Antigonish fault block are dislocated and do not form a neat succession. However, when pieced together like a jigsaw puzzle, they provide an almost continuous record of the geological evolution of this section of Nova Scotia. This can be correlated with parts of Cape Breton, the Cobequid Hills, and other areas further south along the Atlantic seaboard.
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Precambrian Basement Rocks
The oldest rocks are those of the Bass River Complex, found from Economy River to Nuttby and in the Central New Annan area, and the Mount Thom Complex, exposed at Mount Thom. These rocks were originally sedimentary and volcanic deposits but have been metamorphosed to schists and gneisses. They form part of the Precambrian basement upon which deposition took place in the Silurian. Included in this basement are altered granites which were intruded during obscure early phases of crustal upheaval.
Early Geological Events
The oldest strata are of the Precambrian Georgeville Group, which consists of volcanic and sedimentary rocks many thousands of metres thick. These rocks are intruded by fine-grained igneous rocks that are believed to be the necks of ancient volcanoes. Sugarloaf Hill south of Malignant Cove is an example of a volcanic neck. This early period of vulcanism ended with crustal disturbance and metamorphism that may have been part of the Taconic Orogeny during the Ordovician.
Marine Sediments at Arisaig
Between the Taconic and Acadian orogenies (Silurian to Devonian) came a period of continuous deposition in a shallow sea. During this time the Avalon Zone was developing far distant from the Meguma sediments, which had already accumulated off the coast of Africa (or South America). The richly fossiliferous strata which accumulated in this shallow sea are exposed west of Arisaig Point and contain brachiopods, graptolites, pelecypods, trilobites, crinoids, cephalopods, ostracods, and bryozoans. These fossils are well preserved and have been very significant in tracing the history of the Avalon Zone and relating it to other parts of eastern North America.
The succession of strata ended with the shallow accumulation of water-lain deposits. The youngest are the red beds of the Knoydart Formation (exposed along the road between McArras Brook and Dunmaglass, 5 km to the south). These contain the remains of freshwater fish which have been correlated with similar strata in Europe. It appears that the North American and European crustal plates may have drifted together by this time, initiating the formation of Pangaea and the onset of the Acadian Orogeny.
During this orogeny, the pile of sediments was uplifted and granite was intruded. The Pictou-Antigonish block rose along the major fault lines and initially formed a topographic high. Later it became an island in the Carboniferous Sea and was eventually engulfed by Carboniferous sediments. Still later, erosion caused readjustment to take place along the numerous fault lines, which in turn produced a "jumbling" of the strata.
The northern border of the Pictou-Antigonish Highlands is the scarp of the Hollow Fault, which extends from Cape George almost to New Glasgow. Beyond this to the west it joins the Cobequid-Chedabucto Fault. Along the Hollow Fault is a 200-m scarp which has developed as a result of differential erosion since the Tertiary. The old strata of the highlands are much more resistant to erosion than those surrounding them. The scarp is conspicuous south of Piedmont. Further northeast, between Baileys Brook and Doctors Brook, the fault lies in a long, straight valley with a very high, steep southern margin. Along the valley flow the tributaries of several rivers, which turn abruptly northwestwards and drain into the Northumberland Strait. The valley, called "The Hollow" or "Bruin's Highway," has eroded from the softer or broken strata within the fault zone. From Malignant Cove to Cape George, the Hollow Fault forms high cliffs along the straight coastline.
Within the body of the fault block many subsidiary faults crosscut in north-south and northeast-southwest directions. Narrow valleys have formed along some of these lines, particularly where softer strata have been downfaulted, for example, east from Kenzieville. This valley was deepened during the Pleistocene and now contains deposits of sand and gravel which create a uniform grade. Some valleys are ancient landscape features which are now being exhumed as the Carboniferous infilling strata are being stripped away. An example of such a fossil valley is found at Marshy Hope and along the Eden River. Another valley near Kenzieville lies along the length of the Kenzieville Trough - a downfolded section of the Arisaig Formation.
|Cape George Point
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Around the borders of the Pictou-Antigonish Highlands, the prominence of the scarp slope reflects the different hardnesses of adjacent strata. Where soft Windsor sediments are set against the resistant block, the scarp is prominent; where harder Horton strata are juxtaposed, the scarp has a diminished expression.
The southern boundary of the Highlands is the Cobequid-Chedabucto Fault; here the block is set against Horton strata (see Figure 18). The topography of this margin is rugged. The scarp reaches 180 m in places and is cut by deep valleys where other fault lines create lines of weakness; e.g., along Garden River to Eden Lake, and along Moose River, Beaver River, and Campbells Brook. The height of the scarp in part reflects the vertical movement (in addition to the extensive horizontal movement) along this major fault.
The drainage pattern is generally dendritic but is heavily influenced by fault lines. Along the margins, streams and rivers flow down the scarp slope in straight narrow channels. Unlike the Cobequid Hills, there are no wind gaps across the Pictou-Antigonish Highlands as evidence of superimposed drainage. Surface water consists mainly of rivers and streams; there are very few lakes. Conductivity in the streams ranges between 28 and 54 micromhos/cm and pH averages 6.4.
Four major soil associations occur in this area. Cobequid soils occupy the southeastern sector of Pictou County. These are stony loams or sandy loam soils developed on a variety of tills derived from diorite, felsite, syenite, and granite. Barney River soils have developed on shaly loam tills derived principally from Silurian shales, while Kirkmount soils around North Bloomeld have developed on
tills derived from schists, hard sandstones, and slates. Well-drained Thom soils have developed on tills derived from sandstone and hard metamorphic rocks.
Because of the elevation and low evapotranspiration, all these soils tend to have accumulated substantial levels of organic matter in the surface layers. Most are stony and shallow to bedrock. The Barney series is somewhat less stony and is also somewhat finer textured than the others.
Mainly shade-tolerant hardwood forest covers this Unit, with Yellow Birch, Sugar Maple, and American Beech being most common. Red Spruce, White Spruce, Eastern Hemlock, and Balsam Fir are scattered on the upland surfaces and form coniferous stands on the lower slopes and valley bottoms. Red Spruce is less common towards the eastern side of the Unit. White Spruce has colonized old farmlands in the area. As in Unit 311, the shrub layer is diverse and vigorous.
An historical perspective on the evolution of the forests is supplied by C.D. Howe, who wrote in 1912: "This large mass of felsites and syenites ... supports a mixed, thoroughly culled forest. The eastern slopes along the Upper Ohio river southeast of Antigonish are quite abrupt and are covered with a mixed coniferous and hardwood forest in which the hardwoods predominate. On some of the slopes they are in pure stands. The broad tableland between the headwaters of the Ohio river and Black brook is made up of low ridges and depressions, the former being covered chiefly by yellow
birch and the latter by rather inferior red spruce. The soil is thin, and large areas are covered with rock fragments. The flats about the lakes, however, support nearly pure stands of good spruce. The tableland also contains frequent black spruce-fir swamps. The western third of the area is three-quarters hardwood, over half of which is yellow birch, and the remaining portion is about equally divided between red spruce and fir."
This Unit provides a mixture of mature hardwood and softwood habitats and oldfields, with few bogs or lakes. Like the Cobequid Hills, the Pictou-Antigonish Highlands provide very good moose habitat. The Fisher has been reported from this Unit. Although little appears to be known about this area, it may be assumed that wildlife will be relatively abundant.
Freshwater fishes include White Sucker, Brook Trout, sticklebacks, Golden Shiner, Yellow Perch, and Banded killifish.
Highland Scots settled in various locales in this highland area, practising subsistence farming on marginally productive soils. Many of these farmlands were later abandoned and regenerated into the regional forest of the area. Much of this area is managed for forestry.
Sites of Special Interest
- Sugarloaf Hill (south of Malignant Cove) - ancient volcanic neck
- Arisaig Point westwards - well-preserved fossils of brachiopods, graptolites, clams, trilobites, crinoids, cephalopods, ostracods, and plant remains in ancient coastal floodplain
- Cape George to Malignant Cove - cliffs along the Hollow Fault
- Marshy Hope, Eden River - fossil valleys with remnant Carboniferous infilling
- Blue Mountain - good lookoff north along French River
- Clydesdale (IBP Proposed Ecological Site 11) - mature, relatively undisturbed Sugar Maple forest
- the road between McArras Brook and Dunmaglass exposes red beds of the Knoydart Formation
Provincial Parks and Park Reserves
- Beaver Mountain
- James River
- Cape George
Proposed Parks and Protected Areas System includes Natural Landscapes 44a and 44b.
- Highway 347 at the Blue Mountain, Highway 104 along Barneys River, Beaver Mountain Provincial Park
The Avalon and Meguma Zones
Development of the Ancient Landscapes
Soil and Resources
Plants and Resources
Hardwood Forest (Sugar Maple, Yellow Birch, Beech Association)