THE MICROBIOLOGY, MINERALOGY AND GENESIS OF A TONSTEIN

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Abstract
Summary: An account of the Erda tonstein is presented with the conclusion that its formation was the result of soil-forming processes; this is based, in part, on the evidence obtained from the application of micropalaeontological techniques. Aerobic microbiological degradation of organic matter was carried out by organisms believed to show affinity with bacteria, fungi and actinomycetes, and remains of these organisms are included within a colloidal groundmass. The formation of kaolinite macro-crystals in situ from the colloidal medium, and the inclusion of microbiological remains within these crystals, suggest their biochemical mode of origin. The crystal formation occurred at an early stage in the diagenetic history. Comparison of the chemical composition of the Erda tonstein with soil colloids, and with the ash of the durain coal maceral, emphasizes the close association of this tonstein with the coal-forming peats; independent lines of evidence indicate a change in the vegetation. The position of the water table, in conjunction with particular biological and chemical environments is considered to be the controlling factor in the formation of this tonstein. Observations are made on the variable characteristics and chemical compositions of other rocks referred to “tonstein” and suggestions are presented as to their possible modes of formation.