Geology

A very simplified geology of the area - we have much to learn. We would welcome any informed input from others.

articles
The structure of the Loch Creran Dalradian and a new model for the SW Highlands. M. Litherland 1982
https://en.wikipedia.org/wiki/Martin_Litherland

pdf of BONAWE TO CADDERLIE BURN A. J. Highton Extracted from the Geological Conservation Review Volume 17: Caledonian Igneous Rocks of Great Britain Chapter 8: Late Silurian and Devonian granitic intrusions of Scotland

4.4 billion years :

In the beginning there was a big bang! and some millions of years later the earths crust began to cool. In certain parts of the world are rocks that have been dated back to 4.4 billion years [Jack Hills zircons in Australia - it is noted that these rocks have been weathered suggesting that in fact they may have been remarkably stable and affected by winds and rivers at a time that is known for much magma and asteroid activity when rocks were being formed and reformed rather than a time of cool stable crust. This may indicate that the earths crust is in fact older than previously supposed]. In the Northern Hemisphere parts of the Canadian Shield have been found to be around 4.2 billion years old. In the Isua rocks of Greenland there are signs of bacterial life 3.8 billion years ago in sediments.

up to 750 million years ago The Pre-Cambrian period :

In Scotland the oldest rocks are found under the Outer Isles, known as the Lewis complex which are believed to have stabilized around 3200 - 2700 million years old ago. The next block of rock to collide into this was the Moine thrust created around 1100 - 800 million years ago. This takes us down to the Great Glen fault. The rocks beneath Ardchattan are part of the Dalradian mass which were formed in intense compression and heat, relatively recently around 800 - 750 million years ago.
These assorted blocks of land mass are not a single unit but an assortment of collided blocks of cooked compressed rock which joined together in a recognizable sequence when they were all still well below the equator on their travels from the South Pole to the present position.

Dalradian Rocks

The Dalradian rocks made at this time include - from oldest to youngest: Quartzite, Phyllites, re-crystallised Limestone, Slates and mineralised Schists.
Our corner has examples of many of these beyond where the lava flows either did not reach or have been eroded away since. These are metamorphic rocks made from muds, sands and pebbles accumulating in a variety of marine environments. The depth of water and the degree of volcanic activity varied to create the different characteristics. As they moved north the strata became deeply buried and intense heat and pressure worked to produce the range of rocks we can now see and those that underlie the entire area. Folding and shearing produced the variety in our landscape.
The quartzite represent advancing river deltas into shallow seas, bringing white sand in massive quantities. Metamorphism re-crystallised the sandstone into quartzite - where individual sand grains are bound together by more quartz. The resulting rock is very resistant to weathering and erosion, only frost shattering is effective. The largest example of this in our locale is the ridge of Garbh-aird to the west of Ardmucknish bay at Lochnell estate on which Lady Margarets Tower rests.
Associated with this ridge and seen elsewhere around the locality are bands of limestone and steeply inclined phylites
The Benderloch Slide is a huge crustal dislocation which has enabled younger Dalradian formations to be driven northwest over older ones. This slide apparently runs through the Tralee Bay peninsular, through lower Loch Creran and ends up in Ballachulish. A slide is a low angle thrust or fault often occuring over large areas in the Scottish Highlands, which during intense crustal collision enabled rock groupings to dislocate, thus relieving pressure.

around 650 million years ago

Snowball Earth - there is evidence that the whole earth underwent several periods of major glacial influence. At Port Askaig, Islay and the Garvellachs deposits of Tillite have been found.

700 - 510 million years ago Cambrian period:

The continent of Laurentia was formed - northern Scotland was part of a marine shelf - in these shallow waters sand, mud and limestone deposits were made. These are the raw materials of the sedimentary rocks making up the north west mainland.
It was in this era that the deposits that created the limestone rocks of our area were laid down - unlike most limestone these were not from the shells etc of living organisms its far too early. This was a reaction from chemicals in the sea. In the following millions of years they were heated and compressed, folded and lifted to create the rocks that make Lismore so famously green and fertile. There are a surprising number of other small outcrops in our locality.

510 - 440 million years ago The Ordovican Period :

Scotland was still far south of the equator and now part of the floor of the Iapetus Ocean connected to Laurentia. Southern Scotland lay in the deepest water - thick mud currents sand and mud flowed down the continental shelf which were the raw material of rocks to come.

440 - 400 million years ago Silurian Period :

Still located south of the equator at the southern edge of Laurentia with the Iapetus ocean closing fast. At the opposite side of the ocean is the continent of Baltica and the smaller continent of Avalonia where England [on its northern shore] approaches its collision with Scotland. By the end of this period the ocean has died up and the two countries have joined up.

400 million years :

Ben Cruachan and many other similar mountains are created from massive magma movements creating the granite intrusion which dominates the skyline of Ardchattan. The eruptions would have caused cracking which helped to create the glens we see now. Glencoe is regarded to be a super-volcano whose eruption would dace affected the glboe. There are possibly 40 other "super" volcanoes around the world including the dormant one at Yellowstone, Wyoming, USA!

Between 400 and 60 million years ago

there was a period of remarkable stability in comparison to so many parts of the country. This allowed the erosion elements plenty of time to make their mark.

400 - 365 million years ago Devonian Period

The collision of the land masses also resulted in mountain ranges forming in the northern half of scotland known as the Caledonian Mountains. These mountains were probably as high as the Himalayas are today [7-9,000 metres]. What remains is the result of 400 million years of erosion and intermittent periods of uplift. The debris created from the erosion became the sands and gravels of the Devonian rocks as those found in Strathmore.

365 - 290 million years ago Carboniferous Period -

Lying at the same latitute as the equator Scotland was now Tropical. There were volcanic eruptions, creating well known features such as Arthurs seat]. Life was abundant - there were the reptiles that were the forerunners of the dinosaurs, spiders, insects, amphibians, the seas were full of sharks and other fish. The tropical forests and swamps provided the material for Scotlands coal deposits. There have been some remnants of this forest found in Glasgow

290 - 200 million years ago Permian & Triassic Period.

As all the continents merged to create Pangeae and moved further north it moved into an extreme Desert conditions. Scotland lay sandwiched between America and Europe. The rocks created at this time have all the features seen in present day arid deserts including huge dune structures. The oases were home to mammel-like reptiles.

200 - 150 million years ago Jurassic Period -

the fringes of Scotland like our area lay beneath a shallow warm sea at around 40 degrees N [about where Greece is]. This warm subtropical sea was full of life - many marine reptiles like the Icthysaus and the Plesiosaurs. The land masses were home to many dinosauras - so far Skye is the only place where their remains have been found. There are 7 species identified so far.

150 - 65 million years ago Cretaceous Period :

The global rise in the sea level once again covered Scotland in warm shallow water. Our low lying regions were much deeper.
Its important to bear in mind that at any time the land masses were above sea level the erosion forces would have been acting on them. These forces have removed colossal amounts of material. Rocks that are currently at the surface were once 12 miles below the ground - exactly what was above this is not known. The features we see now indicate the massive heat and pressure they have undergone - most have been folded and faulted and angles of 60' are seen, for example in the Quartz's of Tralee point.
where do the faults at Glen Salach fit in?

60 - 0.85 million years: Volcanic Tertiary -

At this time the Dalriadian area is a highly active with a great deal of volcanic activity. The continents are pulling apart with American going west and Europe going East. Most of what will become the Hebridean islands are on the edge of plates and are created as an area of active volcanoes. ALl that remains after the millions of years of erosion are the internal structures and the lava flows. Glencoe, Ben Nevis and Ben Cruachan probably joined up as a caldera - the first being most active and noxious spewing out gaseous magma like Pompeii. Lava flows from Ben Cruachan have shaped the existing landscape in many places - from the Pass of Brander to Kilmelford and skirting around Oban. Ben Lora is one of the more isolated flow remnants. Volcanic vents along what is now Rubh garbh aird have left magma dykes across the point.

last 2 million years ago Quaternary Period :

At this time the whole Scottish mass continued travelling North to its existing location of 56 degrees North. Following the period of intense activity, which profoundly affected the local landscape was another of stability and a huge amount of erosion.

20,000 - 10,000 years ago -

The next major influence on the landscape were the series of Ice Ages. The last to directly effect the locality ended around 11,000 years ago but the effects of the previous ones probably left their mark in the glens. The ice would have been between 1300m and 1800m above sea level in thickness. The pressure of this would have been IMMENSE. There was probably very little water if any left in the Firth of Lorn. It would have all drained out to a depth of about 150 m - the whole area would have been covered in ice - right out to St Kilda where pack ice would have started. Seas, as we know them, would have been way west of that. The Glencoe glaciers flowed in every direction - the Etive glacier was a very significant flow but no one knows why it turns so sharply west at Glen Kinglas. One theory to explain why the magma flow that makes up the Falls of Lora was not scoured out was that the glacier lost a great deal of energy spilling out over the Moss of Achnacree and even over to Ardmucknish Bay. This is described as a Piedmont stage of glacial erosion.

Glacial moraines
Water level North American ice age melt water
how and when were the other rocks made — limestone, quartzite, red sandstone.
what made this area the shape it is - see aerial maps
volcanic activity

Ice age covered the area.

Most of the Benderloch area was beach but when the sea was at a much higher level in relation to the land. Geostatic? pressure has resulted in the ground we all live on being a few metres higher than sea level now.

From the clues we are picking up in our research it is plain that even in the past couple of hundred years the ground water levels have altered. The area around Balure of Shian was once even wetter than now. In the 1841? census it was called the Island of Balure. If you look at the 1755 Roy map and even on the ground you can see that just beyond the 2 cottages across from Shian wood there is a burn which would not take a great increase in seawater level or tidal surge to create a more profound tidal separation like at the Isle of Eriska just a couple of hundred metres along. We have not yet found where the January 11th 2005 Storm surge levels there were.
It would be interesting to create a map here to show the levels of the water around the peninsula.

Mineral Notices and Observations By the Rev Thomas Macknight DDFRSE Read 4th Jan 1817
1914 observations on the mineral geology of Beregonium

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