XIII. Classification of Scottish Carboniferous Olivine Basalts and Mugearites

I.—I ntroduction . F rom the days of Hutton onwards, the Carboniferous basalts of Scotland have been made the subject of geological researches which have gradually become more and more detailed. This is the natural result of three chief causes; the close proximity of the main volcanic areas to three centres of Scottish geological thought in Edinburgh, Glasgow and St. Andrews; the intimate association of the volcanic products with the coals, ironstones, and other deposits of economic value which have been intensively wrought in the Midland Valley of Scotland; and the rapid development of petrographic technique since the microscope was first applied to the study of rocks. Thus increasing numbers of workers from Scottish Universities and Geological Societies have naturally turned their attention to the elucidation of Carboniferous vulcanicity, while the members of the Geological Survey and their collaborators have been confronted by the same problems during the original mapping and subsequent revision of the Scottish Coalfields. The application of the microscope to the study of the rocks enabled the enthusiastic followers of the pioneers to establish a number of ‘types’ which were found to be of common occurrence in different localities; and so a detailed classification arose. At first this classification was used purely for descriptive purposes, but of late years Survey workers in particular, engaged in mapping large areas of Carboniferous basaltic lavas, have distinguished on their maps the outcrops of different types, and in this way much has been learned of the structure of the lava fields and of This 250-word extract was created in the absence of an abstract