Geology in Leonardo’s ‘Virgin of the Rocks’

Steven Wade Veatch (USA) Leonardo da Vinci (1452-1519), considered one of the greatest painters of all time, used his knowledge of geology to inform his art. Leonardo was also noted for his work in sculpture, anatomy, mathematics, architecture, and engineering during the Italian Renaissance (about 1330 to 1450). From a geological perspective, Leonardo da Vinci’s paintings present a realistic portrayal of nature. In his Virgin of the Rocks (1483-1486), on display in the Louvre in Paris (Fig. 1), the geological accuracy is striking (Pizzorusso, 1996). The painting’s subject is both the Virgin and the rocks. The Virgin sits in front of a grotto or cave, various aspects of which, according to geologist Ann Pizzorusso (1996): “… are rendered with astounding geological accuracy. Leonardo has painted a rich earthscape of rock eroded and sculpted by the active geological forces of wind and water. Most of the rock formations … are weathered sandstone, a sedimentary rock”. Fig. 1. Leonardo da Vinci’s Virgin of the Rocks (1483-1486). From his studies of geology, Leonardo learned how the Earth works and improved the realism of his paintings. Location: Louvre, Paris. Oil on panel transferred to canvas. Height: 199cm. Width: 122cm. (The image is in the public domain.) What looks like basalt, an extrusive igneous rock formed by the cooling of lava, appears above Mary’s head and at the top right of the picture. Leonardo even painted the columnar joints formed by the cooling of the rocks. Also, just above her head is a precisely painted … Read More

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Concretions in sandstones of the Inner Hebrides, Scotland

Mark Wilkinson (UK) Concretions are a common feature in many sedimentary rocks, yet they seem sometimes to be misunderstood. So, how do concretions form? As well-studied examples, let’s look at the ones found in some of the sandstones of the Scottish Inner Hebrides, notably the islands of Eigg and Skye. The concretions are found in several formations, but perhaps the largest and most spectacular are in the Valtos Sandstone Formation of the Great Estuarine Group. This was originally named the Concretionary Sandstone Series after the prominent metre-scale concretions. It is Bathonian in age (Middle Jurassic) and is interpreted as having been deposited in a coastal environment. The Great Estuarine Group is becoming famous for its abundant dinosaur footprints and much rarer skeletal material. The concretions themselves vary from spherical to elongate volumes of rock and are typically from around 50cm to one metre or more in diameter. They are also often coalesced into groups (Fig. 1). Inside the concretions, the spaces between the sand grains are filled completely with a calcite cement. The concretions are resistant to weathering compared to the host sandstone, which is fairly soft, so stick out from the cliff in a sometimes rather alarming manner as you walk below them. I’ve been visiting the concretions sporadically for around 30 years and some of the ones that I photographed in the cliffs in the 1980s are now lying loose on the beach. None of them have fallen while I’ve been there, touch wood. Fig 1. Concretions on … Read More

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Clarkia Flora: 16-million-year-old plants offer a window into the past

Margret Steinthorsdottir and Helen K Coxall (Sweden) Near the small town of Clarkia in Shoshone County, Idaho in the USA, exists a rich and unique fossil deposit. The Clarkia fossils, or Clarkia Flora, as the deposit is mostly called due to the abundance of fossil plants, is so well preserved that the assemblage is referred to as a “lagerstätte”, a scientific term reserved for the world’s very finest fossil deposits. The Clarkia fossils are found in sediments that are now known to be about 16 million years old and belong to a period in Earth history called the Miocene. By this time, the (non-avian) dinosaurs were long extinct (the last of these dinosaurs disappeared about 66 million years ago), the Earth’s continents were more or less in the same position as today, and many of the animals and plants would have started looking familiar to modern humans (who emerged much later, about 200,000 years ago). Fig. 1. The entrance to the “Fossil Bowl” motocross racetrack and fossil locality near Clarkia, Idaho. Among the Clarkia fossils can be found various insects, fish and occasionally the remains of small mammals. However, most striking is the wealth of plant fossils in the form of exceptionally well-preserved leaves, nuts, seeds and wood. Impressively, one can find leaves of oak, laurel, pine and birch that look virtually identical to those we find today. If you look quickly when a new fossil is newly exposed from within the host sediments, you may occasionally even see the … Read More

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La Gomera: A short geological guide

Ken Madrell (UK) The island of La Gomera has an area of 370km2, it is 25km in diameter, has a maximum altitude of 1,487m (Alto Garajonay) and is situated approximately 40km west of Tenerife. Unlike the other Canary Islands, La Gomera has experienced a long and continuing eruptive break and is in a ‘postshield erosional stage’. Carracedo and Troll (2016) describe this as the stage when active volcanism has ceased, and erosive and denudational landforms are predominant (p. 39). The submarine base of the island shows that it rests on a shallower ocean bed than the surrounding islands. The emerged land mass is semi-circular in shape, with a radial drainage pattern from its centre near Alto de Garajonay. The dating of the island has proved problematic, as some of the earlier measurements placing its age between 15 Ma and 19 Ma have since proved to be inaccurate. More reliable estimates now put its age at between 10 and 11 Ma. Fig. 1. Roque Argando viewed from Lomo de la Mulata. La Gomera’s general stratigraphy comprises of three main rock sequences: (1) A Miocene basaltic shield, including a basal plutonic complex (that is igneous rock formed by solidification at considerable depth beneath the earth’s surface); (2) A nested felsic (that is, igneous rocks that are relatively rich in elements that form feldspar and quartz) stratovolcano (which is built up of alternating layers of lava and ash); and (3) The youngest Pliocene volcanism. Fig. 2. Sketch map of La Gomera, showing the … Read More

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Volancoes of Big Island, Hawaii (Part 3)

Dr Trevor Watts (UK) This is the last of a three part article about the volcanoes of Big Island, Hawaii. In the first part, I discussed their background and explained some of the terms used to describe the lava that can been seen there. In the second, I discussed some of the highlights that my wife and I saw during our several trips to the island, including in October 2014. And in this part, I will continue to describe what we saw. Fig. 1. One of the kipukas (that is, untouchedby- lava areas of forest). The abandoned lava cliff at Kalapana This is a stretch of old cliff face that is now several hundred metres from the sea. It is located among the flows of February 1992 to October 2003, but the area was re-flooded with lava between 2007 and November 2013, when the ocean entry hereabouts was blocked. The site is just under 5km southwest of present-day Kalapana near Poupou, where the Royal Gardens lava flow reached the coast. The walk is well worth the effort for the variety of lava formations, the many tumuli or blisters of lava, and the coastal scenery along the present cliffs. We were guided here by Gary Sleik, who lives on the lava at Kalapana. Fig. 2. The first section of cliff face, with the lens-shaped tube blocked by cindery flow. The cliffs are backed up by a small kipuka, which is an area that was left untouched, as the lava flowed around … Read More

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Volancoes of Big Island, Hawaii (Part 2)

Dr Trevor Watts (UK) This is the second of a three part article about the volcanoes of Big Island, Hawaii. In the first, I discussed their background and explained some of the terms used to describe the lava that can been seen there. In this part, I will discuss some of the highlights that my wife and I saw during our several trips to the island, including in October 2014. A night walk to the flowing lava from Kalapana This was one of the major highlights of our previous trip in 2013. Several local guides conduct walks across the old lava (mostly 1981 to 2013 flows) to wherever the current flow is best viewed. Our lead guide was Dave Ewing (postewing@gmail.com or (808) 315-2256) and our group met up at his house, located on private properties beyond the “End of the road” signs at Kalapana. This house is one of the very few to survive the 2010 flow, which came through the Royal Gardens subdivision and into Kalapana. Fig. 1. A going away party to mark the long-expected event of the house burning at Kalapana on the night of 25 July 2010. My thanks to Darlene Cripps and Gary Sleik for this picture. We began in late afternoon, with around a dozen people in the group. The walk initially passed the remnants of some of the other homes – a corrugated roof, a fridge, some pilings, and so on, before getting onto the fresh lava. It was almost five kilometres … Read More

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Volancoes of Big Island, Hawaii (Part 1)

Dr Trevor Watts (UK) We (my wife Chris and I) enjoyed our fourth visit to Big Island Hawaii in May 2013 so much that we decided to return to the same places in October 2014. We were hoping to see similar events and activities, which we had found particularly interesting and accessible over the years. Every time we visit, something changes or isn’t possible, but this time was a little more changeable than most. The intervention of three ladies altered a few of our plans – Iselle, the hurricane that visited the southeast of Big Island two months before we arrived; Madame Pele, the Hawaiian Goddess of the Volcano; and Ana, the hurricane that hit the area during our stay. The three interventions illustrate the simple fact that we and our little plans have to be adaptable and show that some of the great locations will be discussed in these articles and will be missed if you only make one visit. This is the first of three articles on Big Island in Hawaii. In them, I will talk about the major highlights of our visit in connection with the volcanic activity of this wonderful island. This first part will mostly illustrate the different volcanic concepts that need to be understood to appreciate what can be seen, and will also provide a general background to the location and the significant summer 2014 flow towards Pahoa. About lava Traditionally, lava is described as pahoehoe or a’a. These are taken to mean ropey … Read More

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What’s so special about South Devon?

Professor John CW Cope (National Museum of Wales, Cardiff UK) Take a trip to the South Devon coast around Easter time and you are bound to come across student parties from universities engaged in fieldwork. What is it about this area that makes it so popular as a centre for this? The simple answer lies in a single word — variety. There is probably no other area in the UK where such a wide variety of rock types and ages is well-exposed in such a small geographical compass. Let’s have a look at some of the factors. The geological succession The oldest rocks exposed in South Devon are of Devonian age and, unlike many other areas of the UK, the Devonian rocks are in marine facies virtually throughout. Looking back over the history of geology, the age of these rocks had initially proved difficult to identify and it was only after Murchison had seen the marine successions in The Rhineland and Russia that he realised that these marine rocks were the equivalent of the Old Red Sandstone farther to the north. The Devonian rocks present a variety of marine facies, with the Middle Devonian limestones being of particular note. The limestones are a local development whose presence, in an otherwise deeper water succession, is due entirely to local shallowing of the water caused by thicknesses of volcanic rocks extruded along extensional fault lines as the local basins developed. This shallowing allowed reef-building organisms to flourish and the principal ones of … Read More

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Giant’s Causeway (Part 2): Other volcanic highlights

Dr Trevor Watts (UK) This is the second and final part of an article on the volcanic highlights of Northern Ireland’s Giant’s Causeway and surrounds. For the first part, see Giant’s Causeway (Part 1): An introduction.) We were in the area for several days and the weather was fairly mixed, but there were glorious skies between the showers, and the high winds brought the waves up beautifully. Of the six highlights discussed below, we visited the first three in one day, as all were a few kilometres to the west of The Giant’s Causeway. Those to the east, we visited on another day. Fig. 1. A map of some of the highlights. They are all supremely interesting and give an idea of the range of volcanic features to be seen. You cannot see an actual, traditional volcano in Antrim, with its classic shape. However, you can visit many scattered and varied elements of the area’s vulcanicity, and so gain an appreciation of the overall picture. Fig. 2. Fanciful cross section of highlights. 1. Deep lava flows forming the Causeway Basalts and their columnar basalt features. Found at The Giant’s Causeway and Ballintoy Harbour. 2. Beds of red ‘laterite’ rocks and soils buried by the later lava flows. Seen along the whole coast, especially east of the Giant’s Causeway. 3. Multiple relatively thin lava flows forming the Lower Basaltic Series. Seen at The Giant’s Causeway area and Dunluce Castle. 4. Dykes bringing magma towards the surface through fissures of cracks in … Read More

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