The igneous geology of the Burntisland district
Allan, Douglas Allan
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The district examined in the course of the research embodied in this paper is the south -eastern part of the county of Fife, lying between the coast towns of Aberdour and Kirkcaldy, and stretching in- land to a roughly semicircular boundary enclosing Auchtertool, Raith and Chapel. The area contained within these limits is approximately thirty square miles, and was mapped on a scale of six inches to the mile, thus embracing the major portion of Sheet 36 and all of Sheet 37 of the 1864 edition of the maps of the Geological Survey on that scale. The revision of the area lately commenced by the Survey will, on account of an alteration in the numbering of the maps, be indicated on part of Sheets 35 and 39, and all of Sheet 40. The results of the present examination of the igneous geology of the area are reproduced at the end of this paper on a scale of two inches to the mile, thus reducing the map to the minimum size consistent with the distinct indication of the rock types represented.The object of this investigation was to examine the microscopic characters and field relation- ships of the igneous rocks which have made the coastal part of this region for long a classic ground for the study of Carboniferous Puy phenomena. As is indica- ted in the next section, previous investigations had been confined largely to generalised descriptions of field occurrences and characteristics. Apart from the preparation of a detailed record, it was hoped that the great thickness of lava -flows to the north- east of Burntisland might yield to a process of zonin that a thorough acquaintance with their types might make the identification of intrusions more readily possible, and that further information might be gained regarding the relation of the volcanic necks to the general scheme. Finally it was desirable that the position of the South Fife vulcanicity should be shown with regard to the similar outbreaks in adjacent areas.As -a result of this investigation, the following points are considered to be established and to represent an advance in the knowledge of the igneous geology of the area.Necks: Eleven previously known necks have been systematically described and a new one located to the east of Aberdour. From the boulders found in the agglomerate of these necks no evidence has been found that any of them are younger than the Lower Carboniferous. From its inclination to the adjacent lava-flows the pipe at King Alexander's Craig may be of later date than the others.Lava -flows: Earlier generalised descriptions and some scattered petrographical notes have been replaced by a detailed examination. The rocks have been identified as basalts of the Dalmeny and Hillhouse types. A third variety has been located and described under the name "basalt of the Kinghorn Type ". The result of this classification of the rocks of the lava -flows on the coast section has been to establish a series of zones on broad lines, and this has been applied to the inland exposures with success. In the variation of the lavas there is a tendency towards decreasing basicity in the later members. Analcite has been determined as a fairly constant minor accessory. Two . of th south of Seafield previously regarded as lava -flows have beet remapped as intrusions, and a similar alteration has been made in the case of several of the exposures in the Raith Mass as well as the long ridge of Pirniss Plantation.Intrusions: The nature of these rocks has been determined by petrographic examination for the first time. They include basalts of the Dalmeny and Hillhouse types, two varieties of teschenites, olivine dolerites, non-olivine-bearing non-olivine-bearing dolerites and quartz dolerites. A number of new occurrences have been mapped and several old ones interpreted differently. Throughout the larger intrusive masses there has been differentiation into a lower zone rich in olivine, a middle zone with both olivine and augite well represented, and an upper strongly felspathic zone.From their arrangement in the field, the order which the intrusions followed seems to have been basalts first, then dolerites, and finally quartz dolerites. It is suggested that the time of their development may have been confined within the limits of the Carboniferous period.