IV.—The Late Palæzoic Alkaline Igneous Rocks of the West of Scotland

Extract

Of late years it has become manifest that the igneous rocks of the Carboniferous in Central Scotland have a distinct alkaline facies. Such rocks as monchiquite, nepheline-basalt, mugearite, kulaite, phonolite, essexite, and teschenite have been described from the Lothians; whilst in the western counties nepheline-phonolite, theralite, mugearite, and teschenite are already known. There is abundant evidence, however, that in the West the alkaline phase is of later date than in the Lothians, and of late Carboniferous or Permian age. In Arran it probably extended into the Triassic, assuming that the stratigraphy which assigns certain rocks to the Triassic is correct. A general account of this connected suite of alkaline rocks, together with the lavas in the Mauchline Basin, to which they can be shown to be genetically related, is given in this paper, which deals only with rocks demonstrably later than the volcanics of the Calciferous Sandstone. The work on which this paper is based was commenced in 1908, and was assisted in 1909 by a grant from the Government Grant Committee of the Royal Society, for which grateful acknowledgment is made. An unfortunate breakdown in health, however, necessitated the postponement of the investigation for nearly a year. It is still incomplete owing to the difficulty of obtaining adequate chemical analyses, without which it is impossible accurately to determine the affinities of some of the rocks. Pending the completion of the detailed work it has been thought advisable to present this preliminary account of an igneous suite of extraordinary variety and interest.