Geophysical Prospection at Caisteal Mac Tuathal, Perthshire
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GEOPHYSICAL PROSPECTION AT CAISTEAL MAC TUATHAL, PERTHSHIRE, SCOTLAND by MICHAEL ROBERT SAMUEL LUKAS (Under the Direction of Ervan Garrison) ABSTRACT Topographic, magnetometry, and ground penetrating radar surveys were conducted at the potential Iron Age hillfort of Caisteal Mac Tuathal in Perthshire, Scotland to determine structural extents within, and propose areas of interest for future studies at, the site This survey concluded the terrace at the base of the southern slope and the area circumscribed by the visible rampart features and cliff faces to be void of potential archaeological anomalies, and no potential structures or entrances were located along the southwestern rampart. However, radar and magnetic anomalies interpreted as a potential structure or “platform”, and an entrance through the rampart, together with a secondary structure were observed along the northwestern rampart. The details of these potential structures are poorly understood because ground-truthing was not conducted during this study. Regardless, this geophysical exploration of Caisteal Mac Tuathal has improved our understanding of the site and structures therein. INDEX WORDS: Shallow Geophysics, Archaeogeophysics, Ground Penetrating Radar, Magnetometry, General Packet Radio Service, Caisteal Mac Tuathal, Drummond Hill, Perthshire, Scotland, Iron Age, Hillfort GEOPHYSICAL PROSPECTION AT CAISTEAL MAC TUATHAL, PERTHSHIRE, SCOTLAND by MICHAEL ROBERT SAMUEL LUKAS B.A., Willamette University, 2013 A Thesis Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment of the Requirements for the Degree MASTER OF SCIENCE ATHENS, GEORGIA 2016 © 2016 Michael R. S. Lukas All Rights Reserved GEOPHYSICAL PROSPECTION AT CAISTEAL MAC TUATHAL, PERTHSHIRE, SCOTLAND by MICHAEL ROBERT SAMUEL LUKAS Major Professor: Ervan Garrison Committee: Jennifer Birch George Brook Electronic Version Approved: Suzanne Barbour Dean of the Graduate School The University of Georgia May 2016 iv Acknowledgements First and foremost, I would like to thank Dr. Ervan Garrison1, Dr. Nicholas Dixon2, and Jackie Hoyt3 for their assistance with data collection in Scotland. Gratitude is also owed to my academic and thesis advisory committee – Dr. Ervan Garrison, Dr. Jennifer Birch4, and Dr. George Brook5 – for their help in the development and pursuance of my thesis topic and studies at the University of Georgia, and to Dr. Dean Goodman6 for his invaluable advice on, and help with, data processing with GPR_Slice. This research was funded in part by the Joseph W. Berg Scholarship in Geophysics Fund and the Gilles and Bernadette Allard Geology Award Fund, both managed by the Department of Geology at the University of Georgia. 1 Department of Geology, University of Georgia, 210 Field Street, Athens, GA, 30602 Department of Anthropology Chair, University of Georgia, 355 S. Jackson Street, Athens, GA, 30602 2 The Scottish Crannog Centre, Kenmore, Loch Tay, Aberfeldy, Perthshire, PH15 2HY, Scotland, UK 3 M.A. Medieval Studies at University of York, King’s Manor, York, YO1 7EP, UK 4 Department of Anthropology, University of Georgia, 355 S. Jackson Street, Athens, GA, 30602 5 Department of Geography, University of Georgia, 210 Field Street, Athens, GA, 30602 6 Geophysical Archaeometry Laboratory, Inc., 20014 Gypsy Ln, Woodland Hills, CA, 91364 v Table of Contents Acknowledgements .............................................................................................................iv List of Figures .................................................................................................................. vii List of Tables ...................................................................................................................... x 1. Objectives ....................................................................................................................... 1 2. Archaeological Context .................................................................................................. 2 2.1. Pre-Roman Iron Age in Scotland ............................................................................. 2 2.2. Celtic Scotland and the Roman Conquest .............................................................. 15 2.3. SM 9156 – Caisteal Mac Tuathal........................................................................... 18 3. Field Conditions ............................................................................................................ 26 4. Methods and Research Design ...................................................................................... 27 4.1. General Packet Radio Service Rover and Global Positioning Systems ................. 27 4.2. Magnetometry ........................................................................................................ 27 4.3. Ground Penetrating Radar...................................................................................... 30 4.4. Ground-truthing ..................................................................................................... 42 6. Results ........................................................................................................................... 43 6.1. Lower Terrace ........................................................................................................ 44 6.2. Upper Terrace ........................................................................................................ 47 7. Discussion and Pre-Ground-truth Conclusions ............................................................. 59 7.1. Comparison to Previous Surveys and New, Pre-ground-truth Conclusions .......... 59 vi 7.2. Proposed Archaeology ........................................................................................... 62 7.3. Caisteal Mac Tuathal, the Loch Tay Crannogs, and Glen Lyon ............................ 64 7.4. Future Studies at Caisteal Mac Tuathal ................................................................. 65 8. Appendices .................................................................................................................... 67 Appendix A: GPR_Slice Data Conversion, Resampling, Velocity Analysis, and 3D Volume Creation Data .................................................................................................. 67 Appendix B: Topographic Correction Data .................................................................. 68 Appendix C: Potential Data Impairment Locations along GPR Lines ......................... 74 9. Plans .............................................................................................................................. 76 9.1. Topography ............................................................................................................ 76 9.2. Magnetometry ........................................................................................................ 78 9.3. GPR ........................................................................................................................ 85 10. Compiled Topo-Corrected Radargrams of the UT Semi-circular Anomalies ............ 90 11. Archive Location ........................................................................................................ 95 12. Bibliography ............................................................................................................... 96 vii List of Figures Figure 1: Site location. (a) Map of the British Isles; (b) Loch Tay and Drummond Hill, Perthshire, Scotland; and (c) potential hillfort of Caisteal Mac Tuathal at Drummond Hill – yellow polygon high-lights the upper terrace (modified after Google, Inc., 2014. Compiled from Christison, 1900; RCAHMS, 1956; Dalland and Wessel, 2011). ........... xii Figure 2: Ceramic-rich regions of the British Iron Age (modified after Cunliffe, 2005:Fig. 5.10). ................................................................................................................................... 5 Figure 3: Predominate settlement types in Early Iron Age Britain, c.2150 BP (modified after Cunliffe, 2005:Fig. 21.6). ........................................................................................... 7 Figure 4: The Scottish Crannog Centre (reproduced with permission of the photographer, Nicholas Dixon). ................................................................................................................. 8 Figure 5: Aisled roundhouse; Machair Leathann. Excavation photograph. Site B fully excavated, looking S. (reproduced with permission: Copyright – Historic Environment Scotland; RCAHMS, 1957) ................................................................................................ 9 Figure 6: Hillfort; Oblique aerial view of Woden Law centered on the fort (reproduced with permission: Crown Copyright - Historic Environment Scotland; RCAHMS, 2015b). ........................................................................................................................................... 10 Figure 7: Broch; Oblique aerial view centered on the Broch of Gurness, taken from the NE (reproduced with permission – Crown Copyright – Historic Environment Scotland; RCHAMS, 2009) .............................................................................................................. 11 Figure 8: Roman conquest in Britain, 1st Century A.D. (modified after Cunliffe, 1999:Fig.198). ................................................................................................................... 16 Figure 9a: Geologic Map of