The Stephanian (Carboniferous) barren measures of the Lons-le-Saunier basin, France, consist of two large groups of rocks. Those of the first group are feldspathic and are the product of the breakdown of denuded parent rock; those of the second group, without feldspar, are derived from soil which had developed on similar parent rocks. Enallaxy is the alternation of these two types. Accumulation of the barren measures can be explained in terms of slow and continuous subsidence. Formation of coal seams, however, requires the conditions resulting from more or less sudden subsidence.

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