Rocks at Spencer’s Island

There is an island called Spencer’s Island just off shore in the north Minas Basin in Nova Scotia, Canada. The same name also applies to the small community on the mainland opposite the island. It is the rocky outcrops along the beach of the mainland that feature here. While the island itself is mainly igneous basalt extruded in the Jurassic period, the steeply dipping strata along the mainland shore are composed of Carboniferous period Cumberland Group rocks (approximately the same type as are found at the famous Joggins Fossil Cliffs further north).

At the moment, I have not managed to find information to explain the details of these rocks but they certainly are interesting to look at. I know that they are composed of sandstones, siltstones, and shale (I didn’t notice any conglomerate or coal which are typical of this rock group). They are rapidly wearing away. They are severely impacted by strong tides and currents especially over the winter months. The outcrops reveal multiple layers of sedimentary deposits which occur in a cyclical way with harder more solid bands alternating with softer finely laminated ones. This reflects the depositional environment which was changing on a regular basis. All the rocks are subject to fine fracturing on a massive scale so that the slightest touch would cause the crumbling fragments to cascade to the beach. Sometimes the weathering process has led to falls of large boulders. Sometimes the outcrop is reduced to fine scree.

It was a very cold, dull, windy, wet day in late May when we visited Spencer’s Beach and we were very glad to discover a delightful beach cafe where we filled up on coffee and clam chowder. The beach was once a busy ship-building yard – famous as the place that built the Mary-Celeste.

North Mountain Basalt at Cap d’Or

 

The brooding basalt cliffs at Cap d'Or in Nova Scotia

Cap d’Or or Cape of Gold on the northern shore of the Minas Basin in Nova Scotia is in fact a misnomer. The golden glints in the cliffs which gave the place its name when Samuel de Champlain saw them in 1604 were really veins of copper. The glistening copper has now been mostly mined out but the cliffs remain absolutely spectacular. On the cold and misty day that I visited, the dark massive faces of rock looked their most brooding and atmospheric, almost like a fantasy backdrop from a Tolkien inspired scene.

The Jurassic period North Mountain Basalt outcropping at Cap d’Or. Basalt was originally molten lava that was extruded onto the surface about 206 million years ago. This happened in a number of episodes, each event giving rise to rock that had a different appearance. This is most easily seen in images 2 and 4 where the colour and texture of the rock at the top of the cliff is different from that at the base of the cliff. Details of the columnar fracturing that occurred as the lava slowly cooled, can be seen most clearly along the shoreline where the waves have washed the rock.

REFERENCES

http://www.davidkjoyceminerals.com/pagefiles/articles_capedor.asp

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 Coce-St. Philip’s, Newfoundland and Labrador. ISBN 978-1-927099-43-8.

Rock Strata from Kimmeridge Cliffs – Part 1

Detail of cliff strata from Kimmeridge Bay

The first selection of photographs taken at Kimmeridge Bay in Dorset, England, yesterday (27 March 2015) showing details of the natural patterns, textures, and colours of the rocks. The rocks are described as rhythmically inter-bedded blocky, organic-poor mudstone and fissile, organic rich shale.

Detail of cliff strata from Kimmeridge Bay

Detail of cliff strata from Kimmeridge Bay

Detail of cliff strata from Kimmeridge Bay

Detail of cliff strata from Kimmeridge Bay

Detail of cliff strata from Kimmeridge Bay

Detail of cliff strata from Kimmeridge Bay

Detail of cliff strata from Kimmeridge Bay

Detail of cliff strata from Kimmeridge Bay

Detail of cliff strata from Kimmeridge Bay

For information about the geology of this location look at:

John C. W. Cope Geology of the Dorset Coast, Geologists’ Association Guide No. 22, Geologists’ Association, 2012, pp 159-167, ISBN978 0900717 61 1.

M. A Woods (compiler) Geology of south Dorset and south-east Devon and its World Heritage Coast, British Geology Survey, NERC, 2011, pp 61 – 67, ISBN 978 085272654 9.

Rocks at Clogher Bay 2

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

This is the second in a series of photographs of rocks at Clogher Bay on the Dingle Peninsula in the West Coast of Ireland, and they belong to the Dunquin Group from the Silurian Period. Clogher Bay is just south along the coast from Ferriters Cove which has featured in earlier postings.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Hopewell Rocks, New Brunswick

Red cliffs at Hopewell Rocks in New Brunswick, CanadaYou don’t have to be a rockhound to be impressed by the spectacular scenery at The Hopewell Rocks. Tall cliffs of sloping red strata rise high above the Bay of Fundy shore, with an abundance of naturally worked shapes, caves, arches, and free-standing pillars of rock called sea stacks. At high tide, people can kayak around the stacks, also known locally as “Flower Pots” because of the groups of full-grown trees that grow on top of them – as they also do right to the cliff edges, with their root systems often clearly visible.  At low tide, it is possible to descend a staircase to the ocean floor itself and explore these geological phenomena close up. Viewing time on the seashore is limited by the enormous and potentially dangerous rise and fall of the tides in this narrower northern neck of the Bay, where in some places, and at certain times, the sea can rise by as much as 56 feet.

At one time, about 600 million years ago, this part of Canada’s New Brunswick Province started its life near the Equator. Here it was subjected to uplifting earth movements that incorporated it into the Appalachian Oregon, an ancient mountain chain that now stretches from New Foundland to Florida. By 360 million years ago, the Appalachian building activities had ended and were followed by predominantly erosional processes.

The rocks exposed at Hopewell originated specifically in that part of the Appalachians called the Caledonian Mountains. Erosion by water and wind about 350 million years ago, in the Lower Carboniferous Period,  steadily wore down the mountains, creating massive volumes of boulders, stones, gravel, sand and mud. Near the highland areas, flash floods tore through the valleys and canyons, washing away loads of eroded sediment and depositing it as stony and gravelly debris. Further from the highlands, sediment formed alluvial plains with sorted layers of sand and mud. The region covered by these terrestrial deposits in present day Atlantic Canada is called the Maritime Basin.

Over time, the coarser material in the erosion deposits on the flood plain became consolidated and cemented together with finer sand and silt. Because the land lay near the equator, the climate was hot and dry. Iron-bearing minerals became oxidised, and the rocks turned into redbeds. The series of red rock layers is now known as the Hopewell Cape Formation; this is the rock exposed in the cliffs and sea stacks at Hopewell today – eventually brought to its current position by Continental Drift, the tectonic movement of continental crustal plates.

In the first instance, the variably-textured sedimentary strata were deposited in horizontal layers. However, earth movements tilted them to angles between 30 and 45 degrees. The tilting of the rocks caused horizontal cracks to form parallel to the bedding planes, and also vertically at right angles to the strata. These lines of weakness in the rocks have become the points of entry for weathering agents – glaciers, tides, snow, ice, and winds. Erosion by these forces widens the cracks and steadily works away at the softer horizontal strata. The expansion of water as it changes to ice is a significant factor in the enlargement of cracks and crevices, and the breaking up the rock. Sandstone is softer than the conglomerate and easy for waves to wear away. The overall result is that broad columns of rock are carved into the cliff face. Undercutting at the cliff base creates caves and arches. Eventually, some columns are completely separated from the cliff face and become sea-stacks or “flower pots”.

Redbeds of alternating tilted layers of conglomerate and sandstone from the Hopewell Cape Formation of the Lower Carboniferous Period in Canada.The erosion activities are on-going. Extreme weather events and storms of recent years may accelerate the processes. The cliff face is gradually receding. Sea stacks eventually collapse and new ones are formed. A sea stack can last as little as 100 years or as long as a thousand. However, there is no need to panic about seeing the sights at Hopewell as soon as possible for fear that they will all disappear into the sea – geologists have calculated that there is enough conglomerate in the Hopewell Cape Formation to make “flower pots” for the next 100,000 years.

A walk along the shore beneath Rhossili Cliffs

Blue tidal pool water and limestone rock face

From the southern sandy shore of Rhossili Beach in Gower, the cliffs tower overhead, bearing the village itself. Sheep with bright red and purple markings nonchalantly graze the craggy upper slopes. Visitors to the Worms Head Causeway are minute figures among the hummocks of a former castle, peering recklessly over the edge to the beach below.

The path down from the village to the beach has been disrupted by last winter’s land slip, and heavy machinery continues to make a new, easier way to the shore. The red earth scars of the recent and many previous movements are visible along the face of the fault-line valley that separates the Carboniferous Limestone Rhossili headland from the greater height of the Old Red Sandstone in Rhossili Down. Boulders litter the beach at this point. Some loose rocks are red sandstones and conglomerates from the Down. Many of the larger boulders are composed of angular limestone fragments (something to do with glaciation I think – maybe till) held together by a crystalline matrix that formed from calcium-rich groundwater percolating  between the stones. Some boulders are huge chunks of Black Rock Limestone or similar from the headland and must weigh many tons.

Standing far out on the shore allows a panoramic view of the cliffs, from the soft red soil and erratic turf of the land slip area, along the bare rock exposed strata of the basal third of the cliffs, to the tidal island of Worms Head beyond. The cliff face is scalloped in and out by early quarrying activities. The distinct diagonal arrangement of the dipping rock layers contrasts with the horizontal colour banding caused by the colonisation of the rock surface between tide levels by organisms with different tolerances to exposure.

In places, tidal pools of strangely blue water skirt the pale, barnacle and mussel encrusted rock. Sand ripples like the lans and grooves of massive fingerprints decorate the beach, and create intricate arrangements around isolated boulders, reminding me of Japanese Zen gardens. Rounded smooth limestone pebbles in caves and alcoves bear fossil Sea Lily stems. And everywhere, sharp-edged fragments on the beach are evidence for the continuous weathering of the cliff face where each rock fall is signified by the fresh exposure of frequently orange-coloured stone

Pictures from an Isle of Portland Walk – Part 2

View from the cliff-top coastal path on the west coast of the Isle of Portland

This is the second stage of my walk around the Isle of Portland in Dorset, U.K. I continued to follow the cliff-top coastal path on the west coast of the island, pausing occasionally to look back along the steep cliffs towards the northern end where Chesil Beach joins it to the mainland. Sometimes, I peered cautiously over the edge to the precipitous layered rocks and steep rockfalls where sea birds in niches peered back at me, and where souls more foolhardy than I clambered down to the shore below. Other times, I kept my foot and my eye turned towards the southern tip of the isle as I admired the details of crumbling fractured rocks capping the vertical cliffs upon which, by comparison, the buildings seemed like miniature models.

View from the cliff-top coastal path on the west coast of the Isle of Portland

View from the cliff-top coastal path on the west coast of the Isle of Portland

View from the cliff-top coastal path on the west coast of the Isle of Portland

View from the cliff-top coastal path on the west coast of the Isle of Portland

View from the cliff-top coastal path on the west coast of the Isle of Portland

View from the cliff-top coastal path on the west coast of the Isle of Portland

View from the cliff-top coastal path on the west coast of the Isle of Portland

View from the cliff-top coastal path on the west coast of the Isle of Portland

View from the cliff-top coastal path on the west coast of the Isle of Portland

View from the cliff-top coastal path on the west coast of the Isle of Portland

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved

Cliffs at Mewslade Bay

Limestone cliff peak with raised beach behind it.

The cliffs at Mewslade Bay on the Gower Peninsula are spectacular. They are formed from High Tor Limestone from the Carboniferous Period. You can see a range of the wonderful shapes of the tall peaks and cliffs that fringe the bay in the gallery below. Click on any picture to enlarge it and to see the photographs as a slide show.

COPYRIGHT JESSICA WINDER 2013

All Rights Reserved

Coloured cliff rock at Studland

Red and orange coloured cliff rock on the seashore at Studland Bay, Dorset, UK, on the Jurassic Coast (1)

Red and yellow stripey cliff rock at Studland provides a bright splash of colour on the seashore, and its soft sandy texture seems an irrisistible surface for carving graffiti.

Click HERE for more posts about Studland Bay.

Coloured rock pattern: Red and yellow strata in the cliffs at Studland Bay, Dorset, UK, on the Jurassic Coast - with carved graffiti (2)

Natural abstract rock pattern: Red and yellow strata in the cliffs at Studland Bay, Dorset, UK, on the Jurassic Coast (3)

Pattern and texture in nature: Red and yellow strata in the cliffs at Studland Bay, Dorset, UK, on the Jurassic Coast - with carved graffiti (4)

Natural rock patterns: Red and yellow strata in the cliffs at Studland Bay, Dorset, UK, on the Jurassic Coast - with burrows excavated by bees or wasps (5)

Rock colour, pattern, and texture: Red and yellow rock strata in the cliffs at Studland Bay, Dorset, UK, on the Jurassic Coast - with carved graffiti (6)

COPYRIGHT JESSICA WINDER 2011

All Rights Reserved