On the Microscopic Structure and Residues Insoluble in Hydrochloric Acid in the Devonian Limestones of South Devon

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Abstract
The complicated nature of Devonian Geology in South Devon is well known. In this paper I shall confine my remarks to the microscopic examination of the limestones, and shall not enter on the stratigraphical and palæontological problems which have been worked out by such geologists as De la Beche, Jukes, Godwin-Austen, Holl, Champernowne, Etheridge, Ussher, Davidson, Whidborne, H. B. Woodward, and others. For the purpose of collecting specimens of limestone to be examined I spent a mouth in South Devon during the summer of 1890, and I desire to express my thanks to Mr. W. A. E. Ussher, of H.M. Geological Survey, for the very ready assistance and friendly advice which he gave me. 2. Detailed Examination of the Organic Structure (a) Hope's Nose Limestones .—At Hope's Nose, near Torquay, there is a quarry opened in limestone of varying light and dark colour, and this is capped by a shaly limestone, which Mr. Ussher regards as belonging to the Calceolen Kalk, “apparently completely inverted upon massive bedded limestone containing Heliolites porosus .” Commencing with the Calceola Beds, as representative of the basement limestones, thin sections, seen through a microscope, show a light grey, finely-crystalline groundmass traversed by fissures filled with calcite. In the groundmass are ferruginous patches and minute rhombohedral crystals, apparently of dolomite. Passing to the limestones below—which, it must be remembered, are assumed to be above the Calceola Beds when in their normal position—thin sections of the lowest beds exposed show them to be composed of broken calcareous fragments, the structure

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