Abstract
EDINBURGH. Royal Society, June 7.—PrOf. F. O. Bower, president, in the chair.—D. Balsillie: The intrusive rocks of the Dundee district. Thes belong to two types, viz. diabases and felsites. The former are generally fine-grained dark masses that contain hypersthene and free quartz, which minerals, along with mono- clinic pyroxene and abundant plagioclase felspar (60 per cent. anorthite), occur in a highly feispathic ground mass. Hornblende, biotite, iron ores, and apatite occur as accessories, the first-mentioned, however, only rarely. Occasionally free quartz disappears, the place of hypersthene being then taken by olivine. As a type of olivine diabase may be cited the large intrusive mass near Newton, west from Auchterhouse station. The hypersthene diabases are characterised by the presence of acid segregation veins that often show beautiful graphic intergrowth of quartz and feispar. Nearly all these basic rocks are much altered, the phenomenon of albitisation being of frequent occurrence, and typically displayed in the diabases of Castle Huntly, west from Dundee. The pink rocks would probably have been classed by the older writers as mica oligoclase porphyrites, which name still sufficiently describes them. Reference was also made to an outcrop of highly solidified ash occurring at Mill of Mains, north of Dundee, that probably marks the site of an old volcanic vent. In discussing the age of the intrusions, the opinion was put forward that these rocks of the Dundee district should be regarded as belonging to the volcanic cycle of Lower Old Red Sandstone times.—F. L. Hitchcock: An identical relation connecting seven vectors.
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Societies and Academies. Nature 105, 666–668 (1920). https://doi.org/10.1038/105666a0
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DOI: https://doi.org/10.1038/105666a0