The British Geological Survey (BGS) has published its historical map collection, which shows in great detail the field mapping that has contributed to the modern day geological map. The historical maps date from the late 19th to the early 20th century. They provide a fascinating insight into the process of field mapping and also provide interesting hand-written notes, which may not have been recorded elsewhere. Further information on these very detailed maps is provided by the BGS.
The maps are split into the old Ordnance Survey County Series sheets, which are numbered using Roman numerals. There are 13 individual sheets covering Arran. You can click on each numbered sheet below to view the maps in high resolution:
Scottish County Series map index reproduced from National Library of Scotland data.