Scotland rocks – a tartan tour of planet Earth

Iain Stewart examined the remarkable geological heritage of Scotland and explored how we protect this magnificent legacy and how best we communicate the importance of the rocks beneath our feet to fellow Scots.

Professor Stewart has a fundamental interest in reaching out the general public and trying to stimulate their interest in geology. He stresses that his numerous television programmes on the subject, however, are entertainment not education – but if people are educated through them that’s a bonus! He considers that Scotland’s rocks are important and should be treasured.

James Hutton FRSE, the ‘Father of Modern Geology’, was a farmer’s son from near Edinburgh. Writing at the time of the Scottish Enlightenment, his 1788 paper, Theory of the Earth, clarified some of the fundamental principles of geology and established the subject as a proper science. Through careful observation of Scottish geology, he realised the importance of the Earth’s internal heat to the perpetual formation of the planet. For Hutton, the Earth should be considered as a physiological system and the heat inside the planet, its engine, moving material around and keeping it alive. His perceptions in the late 18th Century are similar to the Gaia principles today; the Earth as a whole interconnected system. Hutton’s discoveries were extraordinary for the time; the popular explanation being that rocks were solely formed through sedimentary processes where layers are built up over time. His ideas, which later
became know as Plutonism, focused on the notion that the heat in the Earth made some rocks molten, which lead to changes in their structure. One example of this is Glen Tilt in Perthshire which Hutton visited in 1785. He noted the existence of boulders made from metamorphic schist that showed intrusions of pink granite, implying that the granite had been molten and then cooled.

Within Hutton’s theory of Plutonism is the concept of a very long geological timescale with “no vestige of a beginning, no prospect of an end”. At the time of his writing, the standard theological dogma was that the Earth was very young, about 7,000 years old. Hutton considered it to be pointless to discuss the age of the planet because, as a natural system that is constantly changing, there is no beginning and end, just a succession of different worlds. Hutton regarded Siccar Point in Berwickshire as conclusive proof of his geological theories; today it is perhaps the most famous geological location on the planet. Professor Stewart described how at Siccar Point there are two obvious types of rocks; horizontal Old Red Sandstone overlies the older, grey, vertically-upstanding rocks (Silurian greywacke). The older grey rocks are formed from mud laid down on the ocean bed; marine organisms in them how that it is from the deep ocean – over 1000 metres deep. The Old red sandstone rocks are completely different and are derived from sand and gravel laid down in a desert environment. Between the two rock forms there is an irregular erosion surface.

Hutton studied this environment and understood that it would take millions of years for this landscape to form; firstly for the sediments to form, then for these to raise up to the surface, plus the time needed to erode that landscape and then for the next desert landscape to form on top of this. Thus, the basic template of the theory of the planet was devised by Hutton in the late 18th Century and Scottish rocks underpin the understanding of modern geology.

A new global theory of the Earth developed in 1960s, including an understanding of plate tectonics developed by Arthur Holmes at Edinburgh University. He first presented his theories in the 1920s, but his ideas were not widely accepted until the 1960s. Today, his model is the one used in the modern understanding of plate tectonics; the planet exudes heat, causing the surfaces to crack, which creates midocean ridges and spreads a ‘conveyor belt’ of rock across the ocean floor. This new rock cools, becomes more dense and, as it gets older, is so cold and dense that it becomes unstable and sinks back down into the mantle – resembling an elegant planetary recycling system. This system is not just recycling rock, but also gases and water. It is this process that continues to provide us with water and is responsible for our atmosphere. Today, these concepts are known as earth system science.

Professor Stewart commented that when people think of a country, they often have a very clear idea of what defines that country; people pick certain moments from a continuum of history that define the nation. In geological terms, it is difficult to define the age of a country – the rocks under our feet are all part of history and have had an extraordinary journey through a whole series of past ‘Scotlands’. Indeed, in reality, Scotland is made up of fragments of other places and has a complex history. Professor Stewart admitted that, at first glance, rocks can be very boring; they are mostly grey! He cited the example of rocks found in a stone wall in Rhynie in Aberdeenshire which are around 407 million years old. At the time they were formed, the world looked very different; places we now know as America, Mexico, etc. were all located in different parts of the globe and Scotland and England were nowhere
near each other. The rocks at Rhynie are important because, if they are cut and polished, exquisite fossil evidence of stems of plants, including some at cellular level, are clearly evident in the layers of volcanic sinter. These rocks are the earliest evidence of ecosystems and, as such, Rhynie is a site of international importance. Such rocks, therefore, are not just rocks, but portals to the past.

In the mid 1800s, the geologist Roderick Murchison was the Director of the Geological Survey and subscribed to the traditional theory that rocks formed in sedimentary layers with the oldest at the bottom and the youngest on top. Some amateur geologists, including a school teacher, Charles Lapworth, suggested that this wasn’t always the case and quoted the example of Knockan Crag in Assynt, where it appeared that the rocks at the bottom were the younger specimens.

Discussions on the subject continued for decades, as Murchison had no time for these suggestions. However, when he died the Geological Survey was taken over by Archibald Geikie. Geikie decided to put an end to these claims and arranged for a team of experts to visit the area and map the geology with the intention of reinstating the Survey’s reputation as the ‘expert’ geologists. Two experts, Ben Peach and John Horne, visited the outcrop and did indeed discover that, as the amateurs had suggested, the older rock was on top; a lack of fossils in rock indicates an older age. However, they also noticed a narrow band of crushed rock lying between the other layers of rocks; described as a “vast rolling and crushing mill of irresistible power”.

Their discoveries led to the assessment that the order of the layers of rock was being disturbed by a slab of rock being pushed up and over another one through tectonic action; the old rock from lower down was being pushed up and put on top of younger rock. Until this time, theories relating to ‘building’ mountains focused on the notion that they were pushed up from the base; this notion of a sideways thrust creating mountains was therefore a revolutionary thought in geology. Peach, Horne and their team continued to map the area for ten years, in incredible detail. Henry Cadell FRSE also studied the geology of this area and developed a geological experiment which attempted to recreate the Earth’s processes. He showed that forces coming in from the side can push rocks on top of each other and form mountains resembling a layer cake of slices of different aged rocks on top of each other. The structure that these geologists discovered in early 20th-Century Scotland, through their detailed mapping, is now known as the Moine Thrust.

Scotland is one of the best places in the world to study geological formations; geologists have been studying and recording here for centuries. There are many varieties of rocks and the country has been exposed to periods of glaciation in the past. Carbon dioxide (CO2) levels from 400 to 500 million years ago can be ascertained from the chemistry of plants left in vegetation traces. Plants first developed about 450 million years ago in an extremely warm time period, when there was a lot of CO2 in the atmosphere. Plants photosynthesising immediately started to draw down the CO2 and, at the same time, oxygen was being pumped into the atmosphere; CO2 levels went into freefall over the next 50 to 100 million years.

Normally, when vegetation dies it decays and the CO2 is released back to the atmosphere; however, this was not happening and the CO2 was remaining trapped in the root systems, leaves and stems. As such, the atmosphere was becoming less CO2-rich and consequently the air temperature was dropping. Evidence of the Carboniferous period, about 300 million years ago, can be seen in the fossilised tree trunks found on the Fife coast, with carbon still locked in. The changes in atmosphere towards the end of the Carboniferous period led into the Ice Age, with ice sheets nearly reaching tropical areas. In the Carboniferous period, the oxygen-rich atmosphere meant that giant beasts, including dragonflies up to 1.5 metres wide,
were common and, although the Carboniferous period was short-lived, importantly, Scotland’s coal deposits were formed in this period from the preserved vegetation.

The extraction of fossil fuels for human use started in Scotland in the mid 19th Century, when James ‘Paraffin’ Young patented a new extraction process for the oil found in the shale rocks to the west of Edinburgh. For a short time, Scotland was the centre of a global oil industry, before the expansion of the industry in the Middle East meant that Scotland could not longer sustain it in economic terms.

Professor Stewart continued by considering how Scotland’s rocks are protected and treasured today. The first geological map of Scotland shows the diversity of the rocks in the country and Scottish stone has been exported across world throughout the decades; indeed, much of New York was built from Scottish stone. Stone built Scotland; the evidence can be seen in our cities’ streets and stone, as an industry, worked for a living. However, today, many quarries are going out of business, but stone remains important as part of Scotland’s heritage. The Geological Conservation Review (GCR) aims to highlight sites of importance to the international community. These are sites that are scientifically important because they contain exceptional features that are not found elsewhere, or they are sites that are nationally important because they are representative of our history – our ‘Crown Jewels’.

Professor Stewart stated that it would be possible to reconstruct the entire history of Scotland’s ancient past from the GCR sites. There are 834 GCR sites in Scotland, including
Siccar Point and Rhynie, 77% of which are afforded Site of Special Scientific Interest (SSSI) protection, which deters their destruction or impairment from activities such as building works or fossil seekers. However, 23% of Scotland’s GCRs are not protected, including some of the most unusual and important sites. For example: An Corran on Skye, which has some of the earliest dinosaur footprints in the UK; Loch Morar, where contorted rock strata can be seen; and Tyndrum, where there is early evidence of mining. Reasons for a lack of protection include the associated financial costs; more finance has been put towards protecting biodiversity instead. Furthermore some authorities are less willing to award protected status in case it hinders industrial and economic development nearby.

Professor Stewart asked “what do we want to do with our rocks?” The answer isn’t to just protect them and keep them away from people; they have a role to play and should be important in education. Scotland needs to promote geology, understand it and appreciate it, and rocks need to be allowed to communicate their heritage. Global Geoparks are areas of outstanding geology, where the geology underpins the community and is part of the sustainable future of that community. There are currently two Global Geoparks in Scotland – in Shetland and the Northwest Highlands. The process for inclusion is constantly being revised and updated and, in the last round, Lochaber Geopark was considered not to have enough support to continue being a viable Geopark, according to UNESCO’s criteria, and was demoted due to its lack of sustainable investment and salaried staff. The Lochaber Geopark still carries out the same work and functions as a Global Geopark, but is not classed in the official status. The Northwest Highlands and Shetland are due for renewal in late 2013 and indications are that they will face the same issues as Lochaber.

Furthermore, later in 2013, UNESCO is likely to raise the status of Geoparks to the same level as World Heritage Sites; as such there needs to be a change of attitude to make Geoparks important in Scotland and ensure Scotland continues to have a Geopark presence. Professor Stewart commented that almost any part of Scotland could be a Geopark, and countries the world over are queuing up to become Geoparks. However, there is not the same emphasis on their importance in Scotland. He commented that there needs to be a sea-change in terms of attitude to ensure the continued importance of geology in Scotland. It is nearly thirty years since the last geology teacher graduated in Scotland. Moreover, the number of students studying geology at school continues to fall; in 2011, 60 students took Higher Grade Geology and this fell to 17 in 2012. From 2013, Scottish Higher Geology has been discontinued. These low numbers reflect the fact that no geology teachers have been produced for nearly 30 years. In England, however, GCSE and A-Level student numbers are increasing.

On a positive note, Scotland is the first country in the world to develop a geodiversity charter. The Scottish Geodiversity Charter has been signed up to by key organisations such as Scottish Natural Heritage, the British Geological Survey, the Royal Scottish Geographical Society and several local authorities. Professor Stewart emphasised that this is a tremendously encouraging step, but one that now needs to be followed up by resolute action to protect and enhance Scotland’s remarkable geoheritage. Furthermore, Scotland needs more new initiatives to get people interested in the subject. Geology is important not only to Scotland’s cultural and economic history and heritage, but also to its future, as it underpins many vital industries, including tourism, oil and gas. It is also integral to the development of new energy sources; for example, carbon storage and fracking.