XI.— Palaeontological Evidence of the Age of the Craighead Limestone

Abstract

Introductory Remarks. The age of the Craighead Limestone and its precise position in the stratigraphical succession of the Girvan area have recently been called in question by Dr. Ulrich (1) who would consider it as being approximately on the same horizon as the Keisley and Kildare Limestones of Upper Bala age and would even put all of them in the Medinan formation of America which has been usually correlated with the British Llandovery. Following Lapworth, Drs. Peach and Horne in the Geological Survey memoir (2) regarded it as of Upper Llandeilo age, but the fossil lists then given require revision. Recently Mr. Lamont (3, 3a) has pointed out that two lithological, if not stratigraphical, horizons or zones in the Craighead quarries with distinct faunal facies have furnished the fossils which have been described together as from the Craighead Limestone. The field relations of this formation are not easy to determine and have received more than one interpretation. But this paper is solely concerned with studying the palaeontological evidence with the view to determining the age of the bed, and the characters and affinities of the members of the fauna are alone utilized for this object. The large amount of material collected from time to time of late years by Mrs. Gray, Mr. John Smith, Mr. James L. Begg, and others, as well as that in the various Geological Museums enables us now to make a general survey of the fauna and to reach some important conclusions. But the detailed study This 250-word extract was created in the absence of an abstract