(Prepared by the Translator)
Helmbold's detailed study of the classic upper Devonian-lower Mississippian Tanner graywacke of the Harz Mountains is based primarily on analyses of three spot samples from quarries near Scharzfeld.
Quantitative chemical analyses, petrographic description, and quantitative computation of principal constituents including estimates of mineral components of rock fragments, and measurements of sorting, shape, and orientation of grains are presented.
The Tanner graywacke is a hard, tough, poorly sorted gray-green sandstone containing the following constituents (average of three analyzed specimens in volume per cent): quartz—24.6, feldspar—32.1, rock fragments—23.0, and matrix—20. Source rocks that supplied these constituents are estimated as follows (average of three analyzed specimens in volume per cent): igneous rocks—58, metamorphic rocks—29, and sedimentary rocks—13.
The geologic setting, texture, composition, and sedimentary structures, such as graded bedding, indicate that the Tanner graywacke is a deposit of an orogenic belt, derived from the southeast, and deposited largely by periodic turbidity currents.
The poor sorting and poor rounding of the grains, the abundant feldspar and rock fragments, and the postulated mode of origin of the Tanner graywacke agree with qualitative specifications of other graywackes, but its quantitative composition deviates from published analyses of them.