Six Common Kinds of Rock from Ireland Geoschol

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Preface and Acknowledgements, These notes and accompanying rock samples are a teaching resource supplied. free of charge to primary and secondary schools throughout Ireland The notes. aim to give plain facts and explanations for teachers wishing to understand more. about rocks whether they are teaching classes in the examination years of. secondary school or in the early years of primary education The notes also. cover the geology component of Core Unit 1 in the new 2004 syllabus for the. Leaving Certificate Examination in Geography, Please pass the samples around the class and handle them If they get grubby. with use they will respond to gentle scrubbing in warm soapy water. To obtain further copies of this booklet and to ask for extra rock samples visit. www tcd ie geology outreach, Students and staff at the Department of Geology in Trinity College who prepared. the rock samples more than 60 000 pieces in total are grateful to the following. people for their kind permission to collect material. Alan French of Hill Street Quarries Arigna County Leitrim. Eddie Power of Ormonde Brick Ltd Castlecomer County Kilkenny. Luis Grijalva of Whelan s Limestone Quarries Ennis County Clare. Gary Flaherty of Whitemountain Quarry Lisburn County Antrim. Colm Walsh of Walsh s Granite Quarry Stepaside County Dublin. Photograph credits Peter Coxon Figs 10 21 George Sevastopulo Figs 7 19. John Graham Figs 6 8 and Juan Carlos Fig 9, The project has the support of the Royal Irish Academy s Geoscience Committee It was. part funded through a Griffith Geoscience Research Award grant aided by the Department. of Communications Energy and Natural Resources under the Strategy for Science. Technology and Innovation 2006 to 2013 and the National Geoscience Programme 2007. 2013 The views expressed in this study are the author s own and do not necessarily reflect. the views and opinions of the Minister for Communications Energy and Natural Resources. A donation from Quinn Group is gratefully acknowledged. Ian Sanders 2007, Revised second edition published 2007 by the Department of Geology Trinity.
College Dublin,ISBN 0 9521066 6 3, All rights reserved No part of this book may be reproduced or stored in any form by any. means electronic or mechanical without prior written permission of the publisher except. in accordance with the provision of the Copyright Act. Prelude the Great Sugar Loaf Myth,1 Introduction,1 1 Where not to begin 4. 1 2 Handling and storing the rock samples 4, 1 3 Looking at rock in the open finding exposed bedrock 5. 1 4 The Ice Age and the source of the sand and clay 6. 2 The six kinds of rock their sources uses and descriptions 8. sandstone mudstone limestone basalt granite schist. 3 How were the six kinds of rock made, 3 1 Sandstone mudstone and limestone sedimentary rocks 11. sandstone mudstone limestone,sedimentary rocks in general sedimentary layers.
3 2 Basalt and granite igneous rocks 16,basalt granite igneous rocks in general. the chemical composition of magma,the mantle and continental crust as magma sources. 3 3 Schist and metamorphic rocks 22,schist metamorphic rocks in general. metamorphism and mountain building,3 4 Partial melting and the rock cycle 24. 4 Geological time 26,5 The geology of Ireland,5 1 The geological map of Ireland 27.
5 2 Ireland s geological history 28,6 Further interesting things about rocks. 6 1 Life in tropical Carboniferous seas 31,6 2 Making Ireland s mountains by erosion 32. 6 3 Water oil and gas in porous sandstone 34,6 4 Formation of zinc and lead ore in Ireland 36. 6 5 How is the age of granite measured 37, 6 6 How can liquid basalt come out of solid mantle 39. 7 The unifying mechanism plate tectonics 41,tectonics where plates are moving apart.
where plates converge subsidence and uplift,8 Ideas for class work 46. 9 Further information and reading 47,10 Index of technical terms 48. Prelude the Great Sugar Loaf Myth, Some twenty five years ago my daughter showed me a picture in her junior. school text book of the familiar cone shaped summit of the Great Sugar Loaf. Mountain in County Wicklow She was fascinated to learn from the picture s. caption that the mountain had once long ago been an active volcano. The mountain however was never a volcano it acquired its distinctive shape. through erosion The rock from which it is made is particularly hard sandstone. The surrounding rocks are softer and over a long period of time they have been. worn away leaving the more resistant sandstone to stick out as a sharp peak. Today the romantic though erroneous idea of ash and red hot lava spewing. forth over the gentle Wicklow countryside lives on The myth is not easily. dispelled It survives perhaps because of a natural fascination with the. prehistoric past and with the fiery violence of volcanoes. In providing this booklet and accompanying rock samples I aim to explain just. how Ireland s ancient landscape evolved and how the underlying rocks were. made Handling actual pieces of rock will I hope make the explanations more. tangible and reinforce the truth that the rocks are incredibly old that they have. been deeply buried and that some of them did after all come from volcanoes. Geology the study of rocks is more important today than it has ever been The. year 2008 has been designated International Year of Planet Earth IYPE by the. United Nations General Assembly meeting in New York The urgent aim of IYPE. is to foster a global understanding of geology so that we may all become more. keenly aware of what we can do and what we cannot do with the materials of. the Earth fuel water metals if we are to preserve our planet for future. generations,Ian Sanders,September 2007, The Great Sugar Loaf Mountain in County Wicklow pictured above is not an. extinct volcano as its cone shaped appearance might suggest It has a prominent. peak because it is made from a huge block of hard sandstone surrounded by softer. rocks Over a very long period of time erosion has selectively removed the softer. rocks leaving the hard sandstone standing proud Many other mountain peaks in. Ireland have a similar origin to the Great Sugar Loaf Among these are Errigal in. County Donegal Croagh Patrick in County Mayo the Twelve Bens in Connemara. and the Kerry Mountains,1 Introduction,1 1 Where not to begin.
Geography books at school often begin the section on rocks with the theory of. plate tectonics But to start there is probably not the best way to get to. understand geology It is perhaps better to begin by just looking at rocks and. becoming familiar with their characteristics and their uses After this it should be. much easier and more interesting too to learn about how rocks were formed. how old they are and what they tell us about the changing pattern of land and. sea over the great expanse of geological time Only then after getting a basic. feeling for what rocks are about does the elegance of the plate tectonic theory. which weaves together so many different strands of geology come into its own. The plate tectonic theory is the Summary and Conclusions section of the story. not the introduction To kick off with plate tectonics is rather like being told the. ending to a good novel it spoils the fun of seeing the plot unfold. 1 2 Handling and storing the rock samples, Two pieces of each kind of rock are included in the set Additional pieces will be. supplied on request for the cost of postage for as long as stocks remain visit. the website www tcd ie geology outreach for details The rock samples should. be passed around and handled by every member of the class To avoid. confusion each piece has been spotted with coloured paint as follows. Sandstone yellow,Mudstone lilac,Limestone blue,Basalt green. Granite red,Schist orange, Before using the rock samples for the first time check them for sharp jagged. edges These should be rubbed smooth against a rough surface such as a. concrete block to avoid minor cuts and to protect the plastic storage bag. Although the rocks are hard they will become bruised and dusty if they are. allowed to bang against each other The mudstone samples are most vulnerable. and have been packed in a small bag of their own to help preserve them You. might consider storing the rocks in a rigid container such as a biscuit tin or lunch. box or perhaps a specially made wooden tray divided into labelled sections If. the specimens become dirty or greasy from continued handling they may be. cleaned by brushing them in warm soapy water and drying them off with a soft. cloth or paper tissues, 1 3 Looking at rocks in the open finding exposed bedrock. Handling rock samples is a good way to start but it is even better to get out into. the open air and look at rocks in the field Where do rocks occur Believe it or. not wherever you go in Ireland you are never far away from solid rock but you. rarely see it because it is usually just below the surface The next time you pass. a large freshly dug hole in the ground take a closer look You will probably. notice that the hole goes down into brownish sand and clay perhaps with stones. in it This material is usually several metres thick and below it if the hole is deep. enough you will see solid hard rock which is called bedrock Figure 1. Figure 1 Block diagram,showing what lies under,the ground A layer of.
soft sandy clay with,stones a few metres,thick usually covers hard. rock called bedrock, In some places nature has kindly saved us from having to dig a hole if we want. to see solid rock On rocky shores and in cliffs along the coast breaking storm. waves have removed the soft sand and clay and cut into the bedrock see. Figures 2 and 3 Bedrock that is uncovered and visible is said to be exposed. On high ground and mountain tops loose soil has usually been eroded by frost. wind and rain and the bedrock sticks through Similarly bedrock is exposed in. the banks and beds of rivers particularly in gorges and at waterfalls These are. all suitable places to look at rock for yourself provided of course that you take. reasonable care Remember that rocky shores can be very slippery below the. high water mark that freak waves can wash you into the sea and that a rising. tide may cut off your retreat You should take particular care on steep ground on. paths along the tops of cliffs and at the foot of a cliff or steep slope where loose. material may fall on you A number of well tried and tested places to visit are. listed on the Trinity College website www tcd ie geology outreach. In quarries and road cuttings it is not nature but heavy earth moving machinery. that has stripped the covering sand and clay and left the bedrock exposed Five. of the six kinds of rock described in this booklet all but the schist were collected. from quarries The rocks are extracted as raw materials for the construction of. roads and buildings Quarrying is a multi billion euro business that plays a key. role in the Irish economy Unfortunately the use of explosives and heavy. machinery make quarries dangerous places to enter and permission to visit them. will only rarely be given by the owner Many road side exposures of rock are. also dangerous to stop at because of fast moving traffic. 1 4 The Ice Age and the source of the sand and clay. The stony sand and clay that hides the bedrock in many parts of Ireland has an. interesting origin It is linked to a period in the past before about 10 000 years. ago based on carbon 14 dates when the climate was extremely cold During. this period the land was buried for much of the time beneath a thick sheet of ice. rather like Greenland is today It would have been far too cold to live here This. period of icy climatic conditions is known as the Ice Age. The ice sheet was not stationary but moved very slowly spreading outwards. under the huge weight of the snow that fell on it The ice scraped and plucked the. solid bedrock as it edged its way relentlessly forwards and it became very dirty. with all the sand mud and broken stones that got carried along within it. About 10 000 years ago following many thousands of years of bitterly cold. weather the climate improved and the temperature rose When the ice sheet. melted the debris embedded within it was left stranded and became draped in a. blanket of sandy clay with stones across the country These loose materials are. described as glacial deposits because they were dropped by melting ice. Figure 2 A layer of stony sand and clay about three metres thick with hard pale. coloured bedrock below it seen in a cliff at Sutton Dublin The sand clay and. stones were originally trapped in dirty ice that melted a little over 10 000 years ago. They are described as glacial deposits It is unclear why the upper part of the cliff is. stonier than the lower part The bedrock is made of sandstone. In many cliffs around the coast thick glacial deposits can be seen resting on the. bedrock e g Figure 2 In places where the glacial deposits have been removed. it is sometimes possible to see parallel scratches and grooves that were gouged. into the solid bedrock by chunks of stone embedded in the base of the slowly. moving ice sheet Figure 3 In some places the glacial deposits make up the. entire height of the cliff because the bedrock is below sea level. Figure 3 Parallel grooves on the surface of bedrock from which pebbly sand and. Six Common Kinds of Rock from Ireland Fully revised and illustrated second edition Ian Sanders Published by the Department of Geology Trinity College Dublin to mark the International Year of Planet Earth 2008 Preface and Acknowledgements These notes and accompanying rock samples are a teaching resource supplied free of charge to primary and secondary schools throughout Ireland The notes

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