Pebbles at Pleasant Bay

Wet pebbles at the water's edge in Pleasant Bay, Cape Breton Island, NS.

We visited Pleasant Bay on a misty May day. It lies on the Cabot Trail in Cape Breton Island, Nova Scotia, Canada. Pleasant Bay is a small village first settled by Scottish immigrants and is nestled around a picturesque fishing harbour at the foot of steep hills. The Grande Anse River meets the sea at this point and in the background are the headlands and mountains of the Blair River Inlier composed of some of the oldest rocks in the world. The village itself lies on Carboniferous sedimentary rocks but these are less well represented in the pebbles on the beach than the more ancient igneous and metamorphic rocks like granites, gneisses and schists that have been transported downstream from the surrounding highlands. You can compare these smooth rounded wave-worn beach stones with the angular rock fragments lying on the river bed at MacIntosh Brook and the Grand Anse River near Lone Shieling not too far away.

Ebb Traces in the Sand at Rhossili

Natural patterns left by the ebbing tide on a sandy beach

As the tide ebbed at Rhossili beach one day in November, it left acres of natural patterns in the sand where the receding waves had sifted the grains of different weight and colour, and rearranged them into drunken stripes and zigzags.

The Landscape of Inishowen

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The Landscape of Inishowen

The beautiful countryside around Inishowen is featured in many articles and fantastic images by Aidymcglynn: Landscape, hillwalking and nature photography around Ireland. Adrian’s photographs of the hills, beaches, and seascapes most effectively capture and reflect the incredibly interesting geology of the region. It is the shores around Inishowen that are the source of the wonderful beach stones collected and photographed by Noel Tweedie which were mentioned in the earlier posting.

Irish Beach Stones

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Irish Beach Stones

If you are as fascinated by beach stones as I am, you will definitely enjoy looking at the new web site by Noel Tweedie at The 365 Beach Stone Exhibition where he has amassed a great collection of photographs and artwork showing amazing beach stones from the Inishowen area in the north of Ireland. His images reflect the incredible geology of the area.

The Lone Shieling

View of the Lone Sheiling replica shepherd's hut at Lone Shieling

The route known as the Cabot Trail in the Cape Breton Highlands National Park cuts right through some of the oldest rocks in the world as it passes round the northern perimeter of the park between North Mountain and the Grande Anse Valley. These rocks belong to the Blair River Inlier  and are up to one and a half billion years old (Donahoe et al. 2005).  They were pushed up from deep down in the earth’s crust by two major fault lines during the Appalachian mounting building episode so that they now lie adjacent to much younger rocks. The road is steep and winding as it passes through the territory, affording no opportunity to get a closer look at this isolated portion of the Canadian Shield and the ancient supercontinent of Rodinia.

It is, however, possible to pull off the road at a site called The Lone Shieling where a replica shepherd’s hut has been built to commemorate the Scottish heritage of the people who first settled the area after being expelled from the highlands of the Isle of Skye. Contained within the walls of this building and its boundary wall are local rocks, some of which come from the nearby Blair River Inlier. They include pink-grey granulite, banded quartz-feldspar gneiss, and also igneous rocks like the white anorthosite, and dark pink syenite that have been zircon dated to 1,100 to 980 million years ago when they intruded into even older rocks that formed about 1,500 million years ago (Hickman Hild and Barr 2015).

The Lone Shieling shepherd’s hut lies within the only accessible part of an undisturbed 4,000 acres of protected hardwood forest, the largest of its kind in the Canadian Maritimes, and marking the northern limit of growth for many of its plant species. Within the sheltered Grande Anse River Valley 97% of the trees occupying the rich moist soil of lower slopes are deciduous sugar maples (some are 350 years old and 25 metres high) with lower numbers of other species like elm, red spruce, hemlock, yellow birch, white ash, striped maple, red oak. White spruce grows on the stony river banks. Wild flowers, twenty species of ferns, and millions of hardy sugar maple seedlings cover the forest floor. Bracket fungi colonise old wood of trees left to fall. Melting snow from mountains to the south floods the river each year and strips soil from the river bed while bringing down rocks of all kinds. Angular stones of a multiplicity of types, colours, textures, patterns, and geological periods are strewn over the river bed.

REFERENCES

Atlantic Geoscience Society (2001) The Last Billion Years – A Geological History of the Maritime Provinces of Canada, Atlantic Geoscience Society Special Publication No. 15, Nimbus Publishing, ISBN 1-55109-351-0.

Canadian Confederation of Earth Sciences (2014) Four Billion Years and Counting- Canada’s Geological Heritage, Nimbus Publishing, pp 93-97, ISBN 978-1-55109-996-5.

Donohoe, H. V. Jnr, White, C. E., Raeside, R. P. and Fisher, B. E, (2005) Geological Highway Map of Nova Scotia, Third Edition. Atlantic Geoscience Society Special Publication #1.

Hickman Hild, M. and Barr, S. M. (2015) Geology of Nova Scotia, A Field Guide, Touring through time at 48 scenic sites, Boulder Publications, Portugal Cove-St. Philip’s, Newfoundland and Labrador. ISBN 978-1-927099-43-8, pp 30-35.

http://www.pc.gc.ca/eng/pn-np/ns/cbreton/natcul/natcul1/b/i.aspx

Rocks at Presqu’ile

Phyllite rock face on the Cabot Trail in Cape Breton Island

The Cabot Trail road leading to Presqu'ile and Pillar Rock in Cape Breton Island, Nova Scotia, Canada.Presqu’ile means “almost an island” and it refers to a narrow stretch of coastline just off the Cabot Trail in Cape Breton Island, Nova Scotia in Canada. It is nearly separated from the mainland by a long narrow lake. The road passes first along the eastern lake shore before crossing to the western shore; and just on the bend is where a track cuts down to the of the shore of Presqu’ile.  Parallel fault lines run along each side of the lake and one of these extends along the beach between the sea stack Pillar Rock and the mainland, where it has been responsible for interesting changes to the rocks.

Three different rock types originating in different geological periods lie incongruously side by side where they have been brought together by major faulting. Most noticeable is the phyllite rock that forms expansive, pale, gleaming surfaces beneath the highway and extending seawards. This is a metamorphic rock that started life as muddy sediment accumulating late in the Ediacaran or early in the Cambrian period (about 550 to 509 million years ago) on the margin of the ancient micro-continent of Ganderia. It was subsequently converted to shale and, when Ganderia collided with Laurentia in the Silurian period (443 to 418 million years ago), was buried by earth movements at a depth of about 8 kilometres and baked by temperatures as high as 300 degrees centigrade. This resulted in its deformation into phyllite by a realignment of the crystals. It was deformed again when Avalonia collided with Ganderia in the Devonian period (418 to 360 million years ago). Veins of quartz and calcite are common in the phyllite.

The black basalt of the sea stack Pillar Rock, lying just off shore from the phyllite cliffs and separated from them by a fault line, was extruded by volcanic activity in the Devonian period. Looking north-east along the shore, the cliffs are composed of sandstones from the Carboniferous period (360 to 300 mya). This odd juxtaposition of rocks from different periods is (I think) due to thrust faulting.

Mechanical digger moving granite boulders for coastal rip-rap sea defence at Presqu'ileThe weakened area of the fault line is reinforced against erosion by wave action by massive rip-rap boulders of granite obtained from Neil’s Harbour further along the Cabot Trail. There were road maintenance works going on during May, and the activities of heavy plant being used to arrange the boulders on the beach prevented access to the site on my first attempt. The digger had gone when I revisited a few days later and the light proved much more favourable for taking photographs.

REFERENCES

Donohoe, H. V. Jnr, White, C. E., Raeside, R. P. and Fisher, B. E, (2005) Geological Highway Map of Nova Scotia, Third Edition. Atlantic Geoscience Society Special Publication #1.

Hickman Hild, M. and Barr, S. M. (2015) Geology of Nova Scotia, A Field Guide, Touring through time at 48 scenic sites, Boulder Publications, Portugal Cove-St. Philip’s, Newfoundland and Labrador. ISBN 978-1-927099-43-8, pp 84-89.

Atlantic Geoscience Society (2001) The Last Billion Years – A Geological History of the Maritime Provinces of Canada, Atlantic Geoscience Society Special Publication No. 15, Nimbus Publishing, ISBN 1-55109-351-0.

Gabbro at Spur Bay

The rocks at Spur Bay in Guernsey, Channel Islands, are composed of igneous St Peter Port gabbro which was formed from 500 – 550 million years ago in the Cadomian phase of activity. This dark grey rock has characteristic large hornblende crystals that often occur in layers alternating with feldspar at this particular location. The distinct dark crystals also give this rock the common name of  “bird’s eye” gabbro. In fact the gabbro has quite a variable composition, texture and patterning within a relatively small area. Some of the natural patterns have been caused by the infill of later-forming cracks and fractures by different molten rocks such as aplite, and the inclusion of rock fragments within the aplite.

REFERENCES

British Geological Survey Classical areas of British geology: Guernsey, Channel Islands Sheet, 1 (Solid and Drift) Scale 1:25,000. NERC, Crown Copyright 1986.

De Pomerai, M. and Robinson A. 1994 The Rocks and Scenery of Guernsey, illustrated by Nicola Tomlins, Guernsey: La Société Guernsaise, ISBN 0 9518075 2 8, pp 40-42.

Roach, R. A., Topley, C. G., Brown, M., Bland, A. M. and D’Lemos, R. S. 1991. Outline and Guide to the Geology of Guernsey, Itinerary 1 – The St Peter Port Gabbro, 76. Guernsey Museum Monograph No. 3, Gloucestershire: Alan Sutton Publishing. ISBN 1 871560 02 0, pp 45-52.