Page:The Journal of geology (IA journalofgeology21894univers).pdf/257

The Lower Carboniferous Rocks of the east of Scotland have within the last quarter of a century attained great economic and geological interest from the oil-bearing shales they have been found to contain. The district around Edinburgh is one of great complication, and until the operations of the shale mines began large parts of the ground which is usually deeply covered with glacial drift were geologically but imperfectly explored. It is only recently that the chief oil shale districts have been mapped correctly, and the new edition of the geological map of the Edinburgh district, on which I have been engaged for several years tracing out the oil shale outcrops, etc., has only been published within the last six months. A detailed account of the structure of this area has not yet been published, and beyond a few short papers by myself and others in various scientific journals, nothing of importance has been written on this interesting subject.

The Carboniferous system of Scotland is broadly divisible into the following groups:

4. Coal Measures, with the most important coals.
3. Millstone grit, chiefly barren sandstones.
2. Carboniferous Limestone Series, with beds of limestone above and below, and shales, sandstones, etc., interbedded with seams of excellent coal in the center.
1. Calciferous Sandstone Series, with sandstones, estuarine limestones, marls, seams of oil shale and occasional impure coal, the