E R Matheau-Raven (UK) Florida has one of the world’s richest fossil deposits of both terrestrial and marine origin, encompassing over 2,000 known fossil locations. The state is famous for its Pliocene/Pleistocene fossil fauna but also has a rich and diverse Miocene heritage, plus its coastal waters abound with giant Carcharocles megalodon shark teeth, much prized by fossil divers for their value. Fig. 1. Tapir lower jaw. The Thomas Farm site in Gilchrist County, North Central Florida has the largest Miocene mammal deposits east of the Rocky Mountains. It was discovered in 1931 after locals reported what they thought was an Indian burial site and has, for the last 70 years, continually given up its secrets. The fossils from here are dated at 18 million years old and are typiﬁed by many types of mammal, such as the early three-toed horse Nanippus. Fig. 2. Horse upper molar: Equus sp. Florida began to form by a combination of volcanic activity and marine deposition along the northwest portion of Africa over 500 million years ago during the latter part of the Cambrian Period. At about 300 million years ago (during the Upper Carboniferous), the time of the formation of the supercontinent, Pangaea, Florida was sandwiched between what were to become North and South America and Africa. Near the Triassic/Jurassic boundary (210 million years ago), Pangaea began to divide into two major continents, Laurasia (North America, Europe and parts of Asia) and Gondwana (South America, Africa, India, Australia and Antarctica). Fig. 3. Tapir … Read More
Patricia Vickers-Rich , Peter Trusler, Steve Morton, Peter Swinkels and Thomas H Rich (Australia) The “road map” allowing (time) travellers to move across more than 1,000 million years in Namibia is recorded in the rocks of this land. And, it is on display in several museums in Namibia – in Swakopmund, Windhoek, Rosh Pinah and Farm Aar. The old part of the road In drafting the early section of this map, Southern Namibia has been a key region for understanding some of the sights our time traveller will come into contact with, some being the weird organisms called Ediacarans. Since the early days of the twentieth century, when geologists, such as Paul Range, and German soldiers occupying isolated outposts in the Aus region of Southern Namibia, some of these strange fossils were reported. These were the first ‘large’ multicellular organisms that prospered on planet Earth before the development of true animals, and amongst them were the tiny cloudinids. Their fossils are preserved in the thick rock sequences that can be seen along the “time road” in Southern Namibia. These showcase a time in the history of life when there were fundamental and pivotal changes in life occurring, with life transitioning from an enigmatic biota to what we consider normal today. And, at a number of museums in Namibia, including the Swakopmund Museum and the Namibian Geological Survey in Windhoek, several of these intriguing organisms are on show – such as the soft-bodied Ernietta, Pteridinium and Rangea,and the tiny hard shelled … Read More
Deborah Painter (USA) I am an ecologist and general environmental scientist, specialising in transportation, energy and industrial development planning to minimise deleterious environmental impacts. I live in the United States and have also written several articles for this magazine. I appreciate just how important local geology and soil science are in one of the aspects of work I do: researching and writing National Environmental Policy Act documents. This is the third of three articles on how environmental scientists apply this knowledge. Part 1 detailed geology and the hazardous materials site assessment of a property (Fig. 1; see Environmental scientists and geology (Part 1): The first phase of an environmental geology investigation). Part 2 dealt with wetland and water permitting and how geology is important in that process (Fig. 2; see Environmental scientists and geology (Part 2): Geology and soil science in the ‘Wetlands and Waters Permitting’ process in the USA). Fig. 1. Hazardous material releases can have a tremendous impact and must be documented along with plans for remediation. (Credits: Deborah Painter.) Fig. 2. If wetlands are to be impacted, permits must be obtained, along with avoidance and minimisation measures put in place. The impacts must not be significant ones. (Credits: Deborah Painter.) Both of these areas of environmental due diligence are parts of every National Environmental Policy Act document, or “NEPA” document. When I write one of these, I must thoroughly document that these two potential issues – and twenty more – have been examined, and that any remediation … Read More
Ken Brooks (UK) The beach from Rocka-Nore to Pett Level is rich in fossil evidence. Even the most insignificant fossils are important because they provide clues that enable us to reconstruct the ancient environments of this area. Between 100 and 140 million years ago, much of southern England was covered by lakes and lagoons. Rivers flowing from the London area and the west deposited great quantities of sand and silt on extensive flood plains. Molluscs, fish and freshwater sharks lived in the lakes and rivers, while the land was dominated by crocodiles, turtles and dinosaurs. Fig. 1. The Hastings coastline today. Eventually, their fossilised shells, scales, teeth, bones and footprints were preserved in the layers of sediment. Carbonised plants, such as horsetails, ferns, cycads, conifers and tree ferns, indicate that the summers were hot and dry (with frequent fires), followed by wet and humid conditions in wintes. Millions of years later, when Africa collided with the European plate, southeast England was pushed upwards into a vast dome-shaped structure, known as the ‘Wealden anticline’. Since then erosion has removed many layers of rock and exposed the sandstones and clays which now form the cliffs between Hastings and Pett. Fig. 2. Hastings during the Lower Cretaceous (© Stuart Handley). Bones and footprints of Iguanodon are among the most common dinosaur remains, although other very interesting fossils have recently been found in the Hastings area. These include the spines and vertebrae of Polacanthus, a tooth from Baryonyx and quillwort plants still in their … Read More
Alister Cruickshanks (UK) The Norwich Crag at Easton Bavents, Southwold in Suffolk is one of the only locations where mammalian remains from the Pleistocene Epoch can be found, in situ, at an accessible location in the UK. The Norwich Crag splits the Antian and the Baventian. At Easton Bavents South Cliff, the Norwich Crag Shell Bed is missing. Instead, there is a ﬁne gravel layer with laminated clay and sand, which yields occasional remains. This bed is equivalent to the Lower Shell Bed of the North cliff at Easton Bavents, One of the latest theories suggests that this was once a pre-historic fast ﬂowing river, which ﬂowed into a larger estuary that was present at the North Cliff during the Pliocene Era. The North Cliff itself has a stone layer above the Norwich Crag Shell Bed. This bed comprises three main bands: the upper, middle and lower beds, but varies considerably along this stretch of cliff. The Norwich Crag Stone bed is directly below the Baventian Clay, both of which are from the Baventian stage which is 1.55 to 1.6 million years old, from the Pliocene Era. The Norwich Crag Shell Bed is Antian in age, which is 1.6 to 1.7 million years old. Fig. 1. Fine gravel layer with laminated clay and sand. A complete lower mandible of a walrus was discovered in situ after high tides during 1993, by my father and me. At this time, the specimen could not be fully identiﬁed and spent ten years at … Read More
Mike Thorn (UK) If you ask someone to think of Oxford, they will not usually picture warm tropical beaches and azure coral seas. However, go back to the middle Jurassic and you would be hard pushed to find a dreaming spire or student on a bicycle anywhere. At that time, around 160 million years ago, Oxfordshire lay beneath a shallow, tropical seaway at about the same latitude that the southern Mediterranean occupies today. Over the course of the middle Jurassic, this seaway varied in depth, but remained close to nearby land masses from which a lot of sediment was derived (Fig. 1). A great thickness and variety of limestones, sandstones and clays were deposited over several tens of millions of years. Fig. 1. Southern England during the middle Jurassic, 160 million years ago. During the nineteenth and early twentieth centuries, there were many working quarries in the Oxford area, exploiting the abundant clay and limestone for the brick and building stone industries. Quarrymen were frequently paid to look out for fossils and these turned up in abundance, fuelling the academic debates on evolution taking place at the time. Fig. 3. Geological Context for Kirtlington Quarry and Dry Sandford Pit. Sadly, many of these quarries have now been filled in and, for the casual fossil hunter in Oxfordshire, it might seem that there are now few opportunities to collect. However, Kirtlington Quarry and Dry Sandford Pit are two old quarries which are open to the public and at which there is … Read More
Ken Brooks (UK) This is the first of three articles on the geology and fossils in the cliffs and foreshore to the east of Hastings. This one is intended as a field trip. The geology here is all Lower Cretaceous and is some of the best in Britain if you are interested in this period of time. Follow the Hastings seafront eastwards to the ‘Old Town’ and the famous ‘net shops’ in Rock-A-Nore Road. Below the high, sandstone cliffs of the East Hill, you will find the Fishermen’s Museum, the Blue Reef Aquarium (a sea-life centre), a large car park and public toilets. This field trip begins at the last stone groyne and continues along the beach towards Ecclesbourne Glen, nearly one kilometre (half a mile) to the east. The massive sandstone cliffs of the Upper Ashdown Formation are overlain by the shales and sandstones of the Wadhurst Clay. A distinct junction between one horizontal bed of rock and another often marks a period of erosion. This may have been followed by a change in the environmental conditions where a different grade or type of sediment was deposited. In this area, the lower part of the cliff is hidden under a scree slope of broken rocks, but there is one small exposure in situ at beach level. Here, there are flattened branches of carbonised wood lying horizontally within a silty mudstone. These were probably washed into a river or lake, then later covered and compressed by sedimentary layers. The leaves … Read More
Deborah Painter (USA) I am an ecologist and general environmental scientist specialising in transportation, energy and industrial development planning to minimise deleterious environmental impacts. I live in the United States and have also written several articles for this magazine. One of the things I really appreciate is just how important local geology and soil science are in one of the aspects of work I do: delineating wetlands and obtaining permits from regulatory agencies for work in wetlands and waters. This is the second of three articles on how environmental scientists apply this knowledge. The first is entitled Environmental scientists and geology (Part 1): The first phase of an environmental geology investigation. The discharge of dredged or fill material into waters of the USA and most categories of work in navigable water bodies require US Army Corps of Engineers authorisation under Section 404 of the Clean Water Act of 1972. These activities also require Section 401 Clean Water Act permits from their state governments. The Federal definition of “waters of the United States” includes rivers, small streams, bogs, most nontidal wetlands, many lakes, mud flats, bays, the US territorial sea, and even many drainage ditches (Figs. 1, 2 and 3). They do not include isolated, nontidal wetlands with no connection to interstate commerce. However, a state may assert jurisdiction over these isolated wetlands under its Section 401 program, if it chooses. Fig. 1. In New York State, northern white cedar (Thuja occidentalis) is a common nontidal wetland tree. (Credits: Deborah Painter.) … Read More
Dr Kendal Martyn (UK) This article describes several processes producing the shape of crystals. Such processes are illustrated in the most common mineral from the Earth’s surface, quartz. Quartz or “simple” silicon dioxide, is made up of interlocking atoms of silicon and oxygen, arranged into various symmetrical structures depending on pressure and temperature conditions. Such variation in the structure accounts for most of the different minerals discussed below. The presence of these different SiO2 minerals in rocks gives important information about the conditions those rocks were exposed to. Starting rules Minerals are classified by their distinctive structure (atomic arrangement), as well as their chemistry: all the mineralsdescribed below have the same chemical composition but different physical forms, known as polymorphs.Different physical structures are favoured by specific conditions of temperature and pressure (Fig. 1).If conditions favour a change in structure, the old structure may be preserved or a new structure formed,depending on the amount of energy available, the energy needed to make that change and the time available to make that change. Quenching (very rapid cooling) may “freeze in” the old structure. Kinetics (the physical re- arrangement of atoms and bonds) triumphs over thermodynamics (theoretically the energetically most favourable structure).Fig. 1. Diagram showing the stabilities of some (not all) of SiO2 polymorphs under different temperature and pressure conditions. (From the Cambridge University website.) Breaking and reforming atomic connections, a radical rearrangement, needs more energy and requires material to diffuse across the crystal. Such reconstructive transitions will only happen if there is … Read More
Ken Brooks (UK) During the Lower Cretaceous period, between 110 and 145 million years ago, Britain was part of the European land-mass. Southeast England was covered by meandering rivers, extensive ﬂood-plains, lakes and lagoons which extended across to central France. Rivers ﬂowing from the London Uplands and the west brought huge quantities of sand, silt and mud, which were deposited over the whole area. Fig. 1. Starlight Cove These sediments later became the sandstones and clays of the Ashdown Sandstone and Wadhurst Clay within the Hastings Beds. Structures in the rocks, combined with fossil evidence, can be used to reconstruct the ancient environments and communities of this period. For example, the siltstones, clays and sandstones have preserved features such as river channel and ﬂood plain deposits, as well as a rich variety of fossilised plants and animals. Fig. 2. An infilled river channel. The carbonised remains of horse-tails, ferns, cycads, conifers and tree-ferns indicate that Southern England had a sub-tropical climate with seasonal rainfall, perhaps like the Mediterranean today. Freshwater sharks and shellﬁsh lived in the lakes and rivers, while the land was dominated by crocodiles, turtles and dinosaurs. Today, their scales, teeth, bones and footprints may be found along the stretch of beach between Rock-a-Nore and Pett Level. Fig. 3. Crocodile tooth: Goniopholis. Around 100 million years ago, the great weight of the sediments, combined with geological faulting, resulted in a gradual subsidence of the southeast. As a warm, shallow sea began to cover most of England and northern … Read More
The second edition of this guide is written to explain the key concepts of tectonics and rock structures to students and to interested amateurs. I have reviewed a number of Graham Park’s books in recently years (see below) and he is clearly a prolific and excellent writer of books about the earth sciences.
Tony and Anna Gill (UK) The best time to look for fossils in Dorset is after heavy rain and winter storms. These conditions make the cliffs unstable and collapse. High winds produce rough seas, which wash the mud away, leaving the nodules that contain the fossils exposed on the beach. The beginning of November 2005 saw a period of heavy rain and strong winds. This stormy weather continued for several days and on 5 November gale force 10 winds, before a high tide, exposing new material (Fig. 1). Fig. 1. A large landslip, approximately four hundred metres east of Charmouth, contains most of the best fossil horizons. This slip is illustrated with the sea crashing into it (Fig. 2). The large stones in the picture below do not contain any fossils. If they did, they would not be there. The best place to look for smaller fossils is around these large stones. Some of the pyrite ammonites found here can be up to 25cm to 30cm in diameter. Fig. 2. The storm crashing against the cliffs at Charmouth. The flat stones, which are from the Obtusum Shales, sometimes contain the ammonite Asteroceras Planicosta and usually the smaller ammonites Promicroceras Planicosta (Fig. 3). Fig. 3. Charmouth was the seabed in Jurassic times, some 195 million years ago. The football shaped and sized, Stellare Nodules, when broken, contain calcite crystals. Occasionally though, an ammonite can be found inside the larger ones. These ammonites can be up to 50cm across, but unfortunately, most … Read More
Dr Richard J Hubbard (UK) Introduction The Thanet Anticline is an uplifted area forming the northeast corner of Kent and is home to the four coastal towns of Birchington, Margate, Broadstairs and Ramsgate (Fig. 1). Historically, the area has been known as the Isle of Thanet and, in this article, I will look at sediment deposition and erosion around the upstanding anticlinal structure and how shorelines have shifted during the past two thousand years. I will finish with some thoughts about how shorelines might look one hundred years from now. The article is based on material drawn from three guidebooks published by GeoConservation Kent, written by Geoff Downer and myself (see below). Fig. 1. The Isle of Thanet. Sketch map of northeast Kent to show the geography of the Wantsum Channel at the time of the Roman occupation. Today’s shoreline is superimposed with some medieval settlements added for orientation. The Isle of Thanet is elevated and forms an ‘island’ because of the underlying structural geology. Note the location of the offshore seismic line published by Ameen (1995), on which the cross section of Fig. 4 is based. (Figure 87 from The Smugglers Trail, Hubbard & Downer, 2021.) This article has also been written to accompany a book review that was recently published by Deposits (see Book review: The Smugglers Trail – Geology of the Thanet Coastline from Broadstairs to Cliftonville, by Richard Hubbard and Geoff Downer). Thanet has been a high standing area for more than 300 million years and … Read More
Helen Gould (UK) Chemistry is the key to identifying the source of a meteorite. The commonest rock in the Solar System – and on Earth – is basalt. Erupted at mid-ocean ridges and many hotspot volcanoes, it also floors the oceans. However, each of these situations can be identified as geochemically different from one another. Some meteorites have geochemical signatures associated with individual asteroids, being either enriched or poor in specific minerals. The ratios of their minerals are plotted against one another, then the shape and co-ordinates of the plots are cross-referenced to a database. This process has allowed distinct groups of meteorites with similar geochemistry to be identified, suggesting that the meteorites in each cluster plotted came from the same source. There are five sub-groups of achondrites of various chemical composition, including eucrites, diogenites, SNC, lunar achondrites and ureilites. The name means they don’t contain chondrules. Most are of igneous origin, but lunar achondrites resemble fragmental sedimentary rocks. The only “weathering” on the Moon comes from impacting meteorites, but this breaks up rocks and reforms them into breccias – jumbles of jagged fragments fused together. Eucrites Eucrites are basaltic meteorites containing low-calcium proxenite and plagioclase feldspar with metallic iron, troilite (iron sulphide) and silicates. They probably all crystallised at or just below the surface of their source bodies. Fig. x. Eucrite. Diogenites Diogenites consist of calciumpoor pyroxenite, which is an igneous rock resembling the ocean crust. Fig. x.. Diogenite. SNC SNC meteorites have been identified as coming from Mars. … Read More
The Crowood Press are really developing a nice little series of books on the landscape and geology of select regions of the British Isles, and Tony Waltham’s addition to the series about the Peak District is well worth a read. This new one follows the same format as the others – beautiful, full colour photos and diagrams, a fascinating chapter on each of the important geological and geomorphological aspects of the area (including buildings and industry), and an author who knows his stuff and can write it down with an easy and authoritative style.
Thomas H Rich and Patricia Vickers-Rich (Australia) Whether they had horns or not, the ceratopsian “horn faced” dinosaurs are distinctive, not only from other dinosaurs, but all other vertebrates as well, in the structure of their skulls. In addition to the horns, another element of their skeleton, the lower arm bone (called the ulna or elbow bone), unexpectedly is so distinctive that it has provided clear evidence that, 130 million years ago, these very ceratopsians were living in Australia. Prior to that discovery, the ceratopsians were known almost exclusively in the Northern Hemisphere. Just over a century ago, a toothless lower jaw found in Patagonia, Argentina was named Notoceratops, “the southern horned face”. The last time that fossil was seen was a decade later when the world-renowned dinosaur authority, Fredrich von Huene, studied and redescribed that fossil and agreed unreservedly that it was a ceratopsian. Illustrations of that bone strongly support its correct identification as a ceratopsian. However, unfortunately, von Huene is the last person known to have laid eyes on it, and the fossil cannot now be found. Thus, the only ceratopsian previously thought to have come from the Southern Hemisphere, disappeared. When the Victorian dinosaur ulna, which is the subject of this article, was first found at the base of the Arch near Kilcunda (Fig. 1) by Mike Cleeland, Tom’s first guess was that it was some kind of carnivorous dinosaur or theropod. This was because it was a short, stumpy bone, which is so characteristic of the … Read More
Deborah Painter (USA) I am an ecologist and general environmental scientist living in the USA and specialising in transportation, energy and industrial development planning to minimise deleterious environmental impacts. I have also written several articles for this magazine. As such, I appreciate just how much local geology is a vital consideration in many circumstances and especially during one of my routine responsibilities – undertaking a Phase I Hazardous Materials Site Assessment of an industrial or commercial property in the United States. This is the first of three articles on how I and other environmental scientists apply our knowledge of geology in our day to day work. But what is the purpose of these assessments? Companies such as my employer do these to benefit a person or business desiring a loan from a bank to purchase a property or to pay for upgrades. Cities and counties also contract with environmental companies for Phase I Environmental Site Assessments for properties they own and want to improve, or intend to acquire for resale to private parties. For example, city officials may have their eyes on an old former school and grounds as the future site for a new police station, and want to know how expensive it would be to renovate it as opposed to demolishing it to build a new structure. The assessment is done to satisfy the current American Society of Testing and Materials (ASTM) Standard E 1527-13: Standard Practice for Environmental Site Assessments (2013), and the United States Environmental Protection … Read More
This is an ambitious little field guide, which aims to allow amateurs to identify basic rocks and rock formations, for the first time, in a systematic way., as it says: “… using only careful observation, a magnifying glass, a pocket knife – and a bit of patience”.
Stephen Moreton (UK) Our journey around Ireland concludes in Ulster. This comprises Northern Ireland, which is part of the UK, and the counties of Cavan, Donegal and Monaghan, which are part of the Republic of Ireland. As geology is no respecter of politics, the national border is ignored here. I assure my gentle readers that this is not intended as a political statement! The geology consists of metamorphic rocks and granite intrusions in the west, a huge expanse of Tertiary basalt in the eastern half, and a series of Tertiary granite intrusions in the southeast corner. Carboniferous limestone makes an appearance in some places, but is not as well endowed with minerals as further south. Fig. 1. The four regions of the island of Ireland. Fig. 2. Ulster in more detail. Donegal, occupying the northwest corner of the island, has such a varied geology that it has long been a favourite venue for university ﬁeld trips. In spite of this variety, there are few mining sites. Lead has been mined at Glenaboghil, Keeldrum and Glentogher, but these old mines are not noted for specimens. However, minor yellow powdery greenockite occurs at the ﬁrst location and green coatings of pyromorphite at the second. What it lacks in mines, the county makes up for in silicate minerals. The beryl occurrence at Sheshkinnarone is probably the best known. Finger size green and blue-green prisms in a white quartz matrix occur at several spots here. The richest is just outside the garden wall of … Read More
Helen Gould UK) What are meteorites? Lumps of rock left over from the formation of the solar system or “chipped off” planets during major impacts can become trapped in the Earth’s gravitational field and fall as meteorites. The three main types are iron, stony and stony-iron. All of these are discussed in this article. In particular, I consider two important questions: Why are they so important? Because they represent the growth (accretion) of planets, they carry clues to our Solar System’s formation.How do we know we are dealing with a meteorite? Like other rocks, meteorites record events. Most of their minerals are familiar but some have higher or lower concentrations than rocks found on Earth, suggesting an extra-terrestrial origin.Irons Fig. 1. Iron meteorite. Most contain 7-15 wt % of Nickel (Ni) metal, with traces of other minerals. At room temperature, instead of a single mineral, this forms a Widmanstätten structure, whose intergrowth lamellae show two different minerals, one with about 40% Ni, the other with only about 5% Ni, and indicate slow cooling from greater than 700°C. Iron (Fe) meteorites have usually been completely melted, proving they formed in asteroid cores. So even asteroids are differentiated – like the major planets – with a core and mantle which solidified slowly. Widmanstätten patternsAlso known as Thomson structures, these are figures of long nickel–iron crystals, found in the octahedrite iron meteorites and some pallasites. They consist of a fine interleaving of kamacite and taenite bands or ribbons called lamellae.Stony-irons Stony-iron meteorites probably … Read More
I like local geological guides, which aim to get you out and about, visiting areas you might not have known are worth a daytrip. And this is a good example. I sat down and read it cover to cover, as it is only 90 pages long. And I now really want to visit this bit of Kent coastline. Largely concentrating on the Upper Cretaceous Chalk, this guidebook explains and illustrates what seems to be some marvellous geology that can also be explored during what could be a lovely day out on the beach.
Stephen Moreton (UK) In the ﬁrst two articles of this series, we looked at Leinster and Munster. Continuing in a clockwise fashion brings us to Connaught. Some of Ireland’s oldest rocks are to be found here, forming the Ox Mountains. The rugged and mountainous west is dominated by metamorphic rocks and a series of granite intrusions. Inland, Carboniferous limestone prevails. Fig. 1. The four regions of the island of Ireland. Fig. 2. Connaught in more detail. Where the latter abuts Devonian sediments is found the jewel in the crown of Irish mineralogy – Tynagh Mine. This giant polymetallic deposit, near Loughrea in County Galway, was discovered in the 1960s and yielded close to a million tonnes of lead, zinc and copper. Much of this was as sulphides dispersed through black mud ﬁlling a huge depression in the limestone. This was formed by acid from rotting pyrite dissolving the country rock. Extensive oxidation and remobilisation of the primary ores produced hundreds of thousands of tonnes of smithsonite, cerussite, malachite and azurite. Scores of rarer species, such as linarite, anglesite, brochantite, native silver and numerous arsenates were also present. Fig. 3. Malachite, from Tynagh, Co. Galway. 64mm x 35mm botryoidal and stalactitic mass dug out of the tips. Sadly, collectors were slow to learn of this treasure and most was sent to the crusher. By the time they did realise something glorious was going on, most was already turned into smelted metal. A fickle attitude on the part of management did not … Read More
Stephen Moreton (UK) In the second part of our tour of Ireland, we head for Munster, which occupies the southwest corner of the island. Geologically, the rocks are mostly inland Carboniferous shales and limestones, with Devonian sandstones forming the coastal peninsulas. All host mineral localities of note. Fig. 1. The four regions of the island of Ireland. Fig. 2. Munster in more detial. Starting in County Waterford, mineral collectors will tend to head for the copper coast – a group of nineteenth century copper mines centred on the coastal village of Bunmahon. The magnificent crystallised native copper and cuprite these mines yielded in the past are elusive nowadays. On the other hand, post-mining oxidation in the dumps and sea cliff levels and outcrops has produced an array of vividly coloured and sometimes rare secondary minerals. These include connellite, langite, atacamite, botallackite, brochantite, lavendulan and erythrite. The soft, wet, blue and green substances that coat the mine walls are amorphous gels that dehydrate and crumble to powder when removed to a dry environment. They are best left where they are. Fig. 3. Tankardstown Mine, Co. Waterford. The author is examining post-mining deposits of an amorphous copper-bearing gel. Mention should be made of the Croaghaun Hill beryl occurrence inland from the copper mines. In a small outcrop of conglomerate, one of many among the scrub, patches and sprays of slender, sky blue beryl prisms occur in a quartz matrix. Unfortunately, the rock is so tough it defeats even the largest sledgehammer. The … Read More
Jesse Garnett White (USA) “It is no measure of health to be well adjusted to a profoundly sick society” Jiddu Krishnamurti My Great Grandfather and his son both gave me some advice at a very young age. “Never trust anyone that won’t look you in the eye when they shake your hand” and “It’s OK to pick up hitchhikers while travelling the road”. These are all positive suggestions that have proved valuable both in the States and abroad. I’ve made a number of interesting decisions in my life. One I never thought I’d make was moving back to Alaska. I’ve told colleagues, dozens of friends, family members and myself, “I’ll never spend another winter in Fairbanks.”. Learning the lesson of ‘never say never’”, while travelling into the past and future simultaneously has been interesting to say the least. When a friend of 26 years heard the news, he said, “You can’t escape Covid-19, Jesse.” I completely blew that off and forged ahead. Since returning to Alaska, I’ve been fortunate to have worked with a lot of good folks, meet new friends, network, and travel around the interior and Alaska Range. I was blessed to work as a contract geologist at an open pit mine in both development and exploration roles, assist mom-and-pop miners with permitting, create an LLC, and work at what I consider the best pizza place in Alaska. Winter temperatures dipped below -50oF and snow depth at the cabin reached four feet in total. At the time of … Read More
Stephen Moreton (UK) The island of Ireland has much to offer the mineral collector, but is relatively unknown to most. This may in part be due to a lack of published information, although, for years, the troubles in the north also served to deter visitors for many years. This series of articles briefly summarises the principal mineral locations on a region by region basis. Fig. 1. The four regions of the island of Ireland. Fig. 2. Leinster in more detial. As the island is divided into four regions, Leinster, Munster, Connaught and Ulster (Fig. 1), which are in turn subdivided into counties, it seems appropriate to cover the island in this way. As the main ferry terminals for the Irish Republic are in Leinster many a trip to the country will start here. Leinster occupies the southeast region of the island and is the driest (or rather least wet) part of Ireland. Geologically, it offers the largest granite batholith in the British Isles, complete with metamorphic aureole, Carboniferous and Ordovician sediments and a scattering of basic igneous intrusions. County Wicklow dominates the mineral scene in Leinster. Fractures along the margin of the Wicklow granite have acted as conduits for much later mineralising solutions, giving rise to lead/zinc veins. These reach their best development in Glenmalure, Glendasan and Glendalough. Fig. 3. One centimetre spinel law twinned crystals of galena, from North Hero lode, Glendasan, Co. Wicklow. Fine schieferspar calcite and dark brown sphalerite have recently been found in Glendasan, while some … Read More
Helen Gould (UK) Following on from my articles on plate tectonics and the rock cycle, the tables below will hopefully be useful as an aide-mémoire to identify rock samples on your field trips. This table is intended as a field guide for budding geologists. Take it with you – and have fun. Fig. 1. (Right) Breccia; and (Left) Conglomerate. Fig. 2. (Right) Desert sandstone; and (Left) Micaceous sandstone. Fig. 3. (Right) Fliint; and (Left) Chalk. Fig. 4. (Right) Oolitic limestone; and (Left) Crinoidal limestone. Fig. 5. (Right) Siltstone; and (Left) Silt. Fig. 6. (Right) Quartzite; and (Left) Clay. Further reading Introducing Metamorphism, by Ian Sanders, Dunedin Academic Press Ltd, Edinburgh (2018), 148 pages (Paperback), ISBN: 9781780460642. Introducing Mineralogy, by John Mason, Dunedin Academic Press, Edinburgh (2015), 118 pages (Paperback), ISBN: 978-17-80460-28-4. Introducing Volcanology: A Guide to hot rocks, by Dougal Jerram, Dunedin Academic Press Ltd, Edinburgh and London (2011), 118 pages (Paperback), ISBN: 978-19-03544-26-6. Introducing Tectonics, Rock Structures and Mountain Belts, by Graham Park, Dunedin Academic Press, Edinburgh (2012), 132 pages (Paperback), ISBN: 978-19-06716-26-4. Planetary Geology: An Introduction (2nd edition), by Claudio Vita-Finzi and Dominic Fortes, Dunedin, Edinburgh (2015), 206 pages (Paperback), ISBN: 978-17-80460-15-4. Rocks and minerals: The definitive visual guide, by Ronald Louis Bonewitz, Dorling Kindersley (2008), 356 pages (hardback), ISBN: 978-14-05328-31-9. Other articles in this series comprise:Plate tectonics (Part 1): What are they?Plate tectonics (Part 2): A closer lookPlate tectonics (Part 3): The rock cyclePlate tectonics (Part 4): More on the rock cyclePlate tectonics (Part 5): A simple … Read More
After having favourably reviewed the first two books in this three part series, I must admit I was very much looking forward to the publication of this last one. And, of course, I wasn’t disappointed. This is the third in a series of guides to safe and responsible fossil collecting along (this time), the East Dorset coast from the Chalk cliffs at Bat’s Head, across what are some of Dorset’s more remote coastal locations, to Hengistbury Head.
Deborah Painter (US) The Los Angeles Times reported on 5 April 2021 that a magnitude 3.3 earthquake struck around 4:15a.m., followed by a magnitude 4.4 quake 29 minutes later. Several aftershocks followed. Seismologist Lucy Jones of the Lucy Jones Center reported that two quakes were 19.31km deep, with an epicentre around Inglewood, in the Los Angeles Basin. She reported that the movement was thrust, probably not on any mapped fault. Californians scarcely even notice an earthquake of magnitude 3.3 at that depth below the surface. That magnitude on the Richter scale is in the order of a large truck driving rather close by, but probably not intense enough to awaken them from sleep at that hour of the morning while being intense enough to warrant a news item. If one believes television programmes and movies, “The Big One” is going to happen sometime in the near future and part of California is going to slide into the Pacific Ocean and vanish beneath the waves, much like an overloaded barge. The trope of the sinking Golden State gained popularity sometime in the 1960s and should have been thoroughly discredited by now. The film industry helped get this into the general public’s mind and the general public keeps it alive. However, it would be impossible for two reasons: Firstly, tectonics is not going to cause the land to subside as though it were a huge chunk of the crust precariously teetering over the edge of the continent. California is firmly attached to … Read More
Helen Gould (UK) In Plate tectonics (Part 3): The rock cycle, I presented an overview of the relationship between the rock cycle and plate tectonics, and then went on to look more closely at igneous rocks. This time, I want to discuss sedimentary and metamorphic rocks, and review the occurrence of the rock cycle in the Solar System. Sedimentary rocks Sedimentary rocks, by contrast with igneous and metamorphic rocks, have no crystalline structure, being made up of little lumps of non-crystalline material derived from weathering other rocks. However, where they have been built up in horizontal layers, they may contain large-scale structures such as bedding. What are bedding planes? When sedimentary rocks deposited underwater (for example, limestones), they may be periodically exposed to the atmosphere due to tectonic uplift or a fall in sea level, perhaps because water is locked up on land as ice. The fact that it may take a thousand years to deposit a centimetre’s-worth of limestone places bedding planes into a context of millions of years. Fig. 1. Garnet micashist. Fig. 2. Garnet. Limestones are deposited in shallow seas, forming from the rain of billions of shells of sea animals onto the seaﬂoor. Deposition stops if the area is exposed to the air and restarts when the sea covers it again, so a gap (bedding plane) forms. Many sedimentary rocks are laid down underwater and may contain bedding planes. In addition, the grain size, the fossils that are present and other lithological features all may vary … Read More
Helen Gould (UK) What is the rock cycle? Usually, the first thing that budding geologists learn about rocks is that there are three kinds: igneous, sedimentary and metamorphic. These three major kinds are divided up into many different types of rock. For example, marble, slate and metaquartzite are all metamorphic rocks; basalt, granite, obsidian and andesite are all igneous rocks; and limestone, sandstone, clay and siltstone are all sedimentary rocks. What is a rock made of? Rocks are made of minerals. Therefore, particular combinations of minerals help us to identify rocks. Minerals are chemical compounds, consisting of chemical elements, which in turn are made of atomic particles. Who first thought of the rock cycle? James Hutton was the first geologist to propose a cycle of rock creation and change. In 1785, he gave a talk to the Scottish Geological Society in Edinburgh. In it, he suggested that rocks undergo processes that change them from one type of rock into another. He later developed the idea in his book, ‘Theory of the Earth with Proof and Illustrations’. He thought there was a relationship between the three basic rock types: igneous, sedimentary and metamorphic. We now know this is correct. Fig. 1. Agglomerate, Fig. 2. Andesite. However, it was not until this idea was set in a plate tectonics context that it really made sense to geologists. At about the same time, another Scotsman, James Hall, invented experimental geology. He demonstrated the crystallisation of basalt under slow-cooling conditions, and produced marble by … Read More