Geology and Landscape | Fresh Water | Soils | Plants | Animals Cultural Environment | Sites of Interest | Topics & Habitats

This Unit is divited into three sub-Units:
(a) Creignish Hills
(b) North Mountain
(c) Boisdale Hills

Geology and Landscape Development
The North Bras d'Or Uplands are a series of elongated northeast-southwest oriented fault blocks situated on the north side of Bras d'Or Lake. They are composed of Avalon crustal material, predominantly Precambrian in age, which has risen in the landscape. The blocks have moved vertically along fault boundaries and have domed and tilted the surrounding Carboniferous strata (see Figures 8 and 19).

Bornish Hill Click to enlarge

The blocks occupy a central position along the tilted planation surface and generally achieve average elevations which are consistent with that position, about 245-310 m. The elevations are greatest on the southeast side where movement was along faults. They then tilt towards the northwest, declining in elevation and ending in relatively shallow dip-slopes on the northern margins.

The relief along the boundaries of the blocks depends upon the nature of the adjacent Carboniferous deposits. The North Bras d'Or Uplands were once islands in the Carboniferous Sea, were probably engulfed by sediment, but are now eroded out as topographic highs. Some parts of the margins are set against resistant early Carboniferous Horton grits, whereas others lie against the Windsor Group deposits. These softer sediments are easily eroded and expose the resistant Precambrian rocks in maximum relief. Horton sandstones, in contrast, form a resistant continuum and mask the boundary with the older rocks.

Creignish Hills (sub-Unit 313a)
The Creignish Hills occupy the same relative position on the planation surface as the Pictou-Antigonish Highlands and achieve an average elevation of 275 m. This block is divided into two almost equal sections of metamorphosed volcanic and sedimentary rocks and granite; the former is Precambrian and the latter is Ordovician.

The northern margin is against Horton grits, which form a rolling upland and topographically mask this boundary. The southern boundary is faulted from Whycocomagh Bay to River Denys Mountain and forms a steep scarp slope against the adjacent Windsor Group deposits.

The profile of the North Bras d'Or Uplands as seen from near Port Hawkesbury is relatively even and dominates the first view of Cape Breton from the causeway.

North Mountain (sub-Unit 313b)
North Mountain lies on the west side of Bras d'Or Lake between Denys Basin and West Bay. It is about 260 m high and is composed of Precambrian granitic and George River Group rocks. The latter originally contained limestone bands, which have been metamorphosed into marble. Some marble is still quarried at Marble Mountain.

The North Mountain block was outside the early Carboniferous basin where the Horton strata were deposited. Later on, during Windsor time, when the sea covered a wider area, the North Mountain block became an island against which Windsor Group strata accumulated. The block is now almost entirely surrounded by Windsor deposits, which are deeply eroded and give maximum relief on both the north and south sides. The scarp is steepest on the south side and forms cliffs along West Bay. The more gentle dip-slope reaches Denys Basin at a shallower angle. The block is crosscut by a fault, forming a narrow, steep-sided valley.

Boisdale Hills (sub-Unit 313c)
This part of the North Bras d'Or Uplands lies on the east side of Bras d'Or Lake and has a more complex geological composition than either the Creignish Hills or North Mountain. The strata include late Precambrian sediments and volcanics, granites of Precambrian and Devonian age, and younger volcanic and sedimentary rocks.

This upland block is crosscut by northeast-southwest oriented faults which divide it into a series of strips. Precambrian granites and George River Group rocks are thus juxtaposed against Cambrian and middle Devonian strata. The fault lines are eroded to form scarp slopes in several places along the coast and inland. A well-developed fault scarp can be seen at Eskasoni; another is aligned southwest and northeast along East Bay.

The Carboniferous strata immediately adjacent to the older rocks are the sandstones and shales of the Grantmire Formation. These are intermediate in erodibility and provide moderate relief next to the harder upland strata.

Fresh Water
There are few lakes, and most of the streams and rivers are tributaries feeding larger rivers in the surrounding District 560. Colluvial deposits in stream valleys are zones of springs and groundwater seeps.

Creignish Hills sub-Unit 313a)
The hills form a divide across western Cape Breton. Both the south-flowing Inhabitants River and the north-flowing Mabou River rise in these hills.

North Mountain (sub-Unit 313b)
The valley is occupied by two streams, Kennedys Brook and MacIntyres Brook. Lakes, bogs, and wandering streams are found on the relatively flat crest of North Mountain, but once the marginal slopes are reached, the streams become straight and fast flowing.

Boisdale Hills (sub-Unit 313c)
The landscape is divided into numerous tertiary watersheds that drain many short streams and small lakes.

Soils
A wide variety of metamorphic and granitic rocks occurs in this Unit, but the strong podzol development and the presence of a thick iron humate B horizon typical of ferro-humic podzols tend to mask the diversity of the parent materials. The principal soil, which has developed from the thin mantle of stony loam till is Thom - a well-drained, stony, sandy loam. Small areas of peat are found in depressions. On the Boisdale Hills (sub-Unit 313c), Mira soils (mottled, sandy loam) have developed where drainage is impeded by relief. There are also some coarse-textured Debert soils. Shallow soils occur on ridges and steep slopes.

Plants
Sugar Maple, Yellow Birch, American Beech,

Alder Brook Ravine Click to enlarge

and shade-intolerant hardwoods occupy the upper slopes and high ridges, while Balsam Fir, White Spruce, and Black Spruce cover the upland flats and ravine slopes. On the Boisdale Hills (sub-Unit 313c), where elevations are somewhat lower (200 m), mixedwoods become more prevalent.

Animals
Little direct study has been done in this Unit, but the small amount of information available for sub-Unit 313c indicates the fauna in Unit 313 is not necessarily similar to that in Units 311 and 312.

Of special note are the large number of eagle nests in stream ravines in sub-Unit 313c. Deer use the side slopes for winter yards; the slopes shelter them, especially on sunny days when the slopes block winter winds. There are few to no moose in this area. Fish include Brook Trout, Golden Shiner, White Sucker, White Perch, sticklebacks, and Banded killifish.

Cultural Environment

Creignish Hills (sub-Unit 313a)
Bornish Hills, a section of the Creignish Hills, is a protected site under the Special Places Act administered by the Department of Natural Resources.

North Mountain (sub-Unit 313b)
North Mountain was well known for its Marble Mountain limestone quarry. The story of this limestone and marble quarry industry of the late 1800s and early 1900s is documented at the Marble Mountain Museum. After limestone was extracted from the quarry, it was crushed, slaked, and shipped to Prince Edward Island, where farmers used it to lime soils. Important Mi'kmaq burial sites are found in North Mountain cliffs bordering the Bras d'Or Lake.

Boisdale Hills (sub-Unit 313c)
Forestry has been one of the dominant land uses in the Boisdale Hills. A limestone quarry once operated here.

Sites of Special Interest

• Marble Mountain - marble quarry

Provincial Parks and Park Reserves

• Marble Mountain
• Barachois
• Eskasoni fault scarp
• East Bay fault scarp

Proposed Parks and Protected Areas System includes Natural Landscapes 49a and 49b.

Ecological Reserves

• Bornish Hill Nature Reserve (sub-Unit 313a)

Scenic Viewpoints

• Marble Mountain (sub-Unit 313b)

Associated Topics T2.2 The Avalon and Meguma Zones T2.4 The Carboniferous Basin T3.1 Development of the Ancient Landscapes T11.4 Birds of Prey T12.3 Geology and Resources

Associated Habitats H3.1 Freshwater Open-Water Lotic H3.3 Freshwater Bottom Lotic H3.5 Freshwater Water's Edge Lotic H4.1 Bog H6.1 Hardwood Forest (Sugar Maple, Yellow Birch, Beech Association) H6.2 Softwood Forest (Spruce, Fir Association)